Kivy label değiştirilmiyor

from kivy.app import App.
from kivy.uix.boxlayout import BoxLayout.
from kivy.uix.label import Label.
from kivy.uix.button import Button.
import sqlite3.
import sys.
import random.
from kivy.clock import Clock.

class MyApp(App):
 #center_label = Label(text='Orta Etiket', halign='center', valign='middle')

 def build(self):
 layout = BoxLayout(orientation='vertical')

 top_labels_layout = BoxLayout(orientation='horizontal')
 label1 = Label(text='Üst Etiket 1')
 label2 = Label(text='Üst Etiket 2')
 top_labels_layout.add_widget(label1)
 top_labels_layout.add_widget(label2)

 center_label = Label(text='Orta ', halign='center', valign='middle')

 bottom_buttons_layout = BoxLayout(orientation='horizontal')
 for i in range(4):
 bottom_buttons_layout.add_widget(Button(text=f'Düğme {i + 1}'))

 layout.add_widget(top_labels_layout)
 layout.add_widget(center_label)
 layout.add_widget(bottom_buttons_layout)
 return layout.
 # Label'ın metnini güncelle.

 #center_label.text = "merhaba"

 def changetextcenter(self, text):
 self.center_label = Label(text=text, halign='center', valign='middle')

if __name__ == '__main__':
 my_app = MyApp()
 my_app.run()
 # my_app.build()
 # Clock.schedule_interval(update_label_text, 5)
x = 0
y = 0
truecount = 0
falsecount = 0
x = random.randrange(1, 100)
# Pencereyi aç.
conn = sqlite3.connect("englishwords.db")
cursor = conn.execute("SELECT*FROM words WHERE id = ? ", (x,))
datas = cursor.fetchall()
for data in datas:
 my_app = MyApp()
 my_app.changetextcenter(data[1])
 # my_app.center_label.text=data[1]
 print(data[1])

print(datas[0])