Проблема с pyqt5

Не получается обрезать виджет, после каждого обновления виджета, почему-то он обрезается, только когда кликаю по кнопке создать изображение второй раз. Что может быть не так?

import sys


from PyQt5.QtGui import QPainter, QColor
from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5.QtWidgets import QApplication, QMainWindow


class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(310, 140)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.verticalLayout_3 = QtWidgets.QVBoxLayout(self.centralwidget)
        self.verticalLayout_3.setObjectName("verticalLayout_3")
        self.widget = QtWidgets.QWidget(self.centralwidget)
        self.widget.setMinimumSize(QtCore.QSize(310, 0))
        self.widget.setMaximumSize(QtCore.QSize(16777215, 100))
        self.widget.setObjectName("widget")
        self.horizontalLayout_2 = QtWidgets.QHBoxLayout(self.widget)
        self.horizontalLayout_2.setObjectName("horizontalLayout_2")
        self.horizontalLayout = QtWidgets.QHBoxLayout()
        self.horizontalLayout.setObjectName("horizontalLayout")
        self.pushButton = QtWidgets.QPushButton(self.widget)
        font = QtGui.QFont()
        font.setPointSize(10)
        self.pushButton.setFont(font)
        self.pushButton.setObjectName("pushButton")
        self.horizontalLayout.addWidget(self.pushButton)
        self.verticalLayout = QtWidgets.QVBoxLayout()
        self.verticalLayout.setObjectName("verticalLayout")
        self.label = QtWidgets.QLabel(self.widget)
        font = QtGui.QFont()
        font.setPointSize(10)
        self.label.setFont(font)
        self.label.setObjectName("label")
        self.verticalLayout.addWidget(self.label)
        self.label_2 = QtWidgets.QLabel(self.widget)
        font = QtGui.QFont()
        font.setPointSize(10)
        self.label_2.setFont(font)
        self.label_2.setLayoutDirection(QtCore.Qt.LeftToRight)
        self.label_2.setObjectName("label_2")
        self.verticalLayout.addWidget(self.label_2)
        self.label_3 = QtWidgets.QLabel(self.widget)
        font = QtGui.QFont()
        font.setPointSize(10)
        self.label_3.setFont(font)
        self.label_3.setObjectName("label_3")
        self.verticalLayout.addWidget(self.label_3)
        self.horizontalLayout.addLayout(self.verticalLayout)
        self.verticalLayout_2 = QtWidgets.QVBoxLayout()
        self.verticalLayout_2.setSizeConstraint(
            QtWidgets.QLayout.SetMinimumSize)
        self.verticalLayout_2.setObjectName("verticalLayout_2")
        self.lineEdit = QtWidgets.QLineEdit(self.widget)
        self.lineEdit.setLayoutDirection(QtCore.Qt.LeftToRight)
        self.lineEdit.setText("")
        self.lineEdit.setObjectName("lineEdit")
        self.verticalLayout_2.addWidget(self.lineEdit)
        self.lineEdit_2 = QtWidgets.QLineEdit(self.widget)
        self.lineEdit_2.setObjectName("lineEdit_2")
        self.verticalLayout_2.addWidget(self.lineEdit_2)
        self.lineEdit_3 = QtWidgets.QLineEdit(self.widget)
        self.lineEdit_3.setObjectName("lineEdit_3")
        self.verticalLayout_2.addWidget(self.lineEdit_3)
        self.horizontalLayout.addLayout(self.verticalLayout_2)
        self.horizontalLayout_2.addLayout(self.horizontalLayout)
        self.verticalLayout_3.addWidget(self.widget)
        self.label_4 = QtWidgets.QLabel(self.centralwidget)
        self.label_4.setObjectName("label_4")
        self.verticalLayout_3.addWidget(self.label_4)
        MainWindow.setCentralWidget(self.centralwidget)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.pushButton.setText(_translate("MainWindow", "Показать"))
        self.label.setText(_translate("MainWindow", "side"))
        self.label_2.setText(_translate("MainWindow", "coeff"))
        self.label_3.setText(_translate("MainWindow", "n"))
        self.label_4.setText(_translate("MainWindow", "TextLabel"))


class MyWidget(QMainWindow, Ui_MainWindow):
    def __init__(self):
        super().__init__()
        self.setupUi(self)
        self.do_paint = False
        self.pushButton.clicked.connect(self.paint)
        self.label_4.setText("")

    def paintEvent(self, event):
        if self.do_paint:
            if self.lineEdit.text() != "" and self.lineEdit_2.text() != "" and self.lineEdit_3.text() != "":
                self.label_4.setText("")
                self.update()
                self.pix = QtGui.QPixmap(
                    int(self.lineEdit.text()) + 10, int(self.lineEdit.text()) + 10)
                self.pix.fill(QColor(240, 240, 240))
                qp = QPainter(self.pix)
                self.draw_flag(qp)
                self.label_4.setPixmap(self.pix)

    def paint(self):
        self.do_paint = True
        self.repaint()
        self.do_paint = False
        self.resize(self.minimumSizeHint())

    def draw_flag(self, qp):
        qp.setPen(QColor(255, 0, 0))
        self.side = int(self.lineEdit.text())
        qp.drawRect(5, 5, self.side, self.side)


if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = MyWidget()
    ex.show()
    sys.exit(app.exec_())