Graphics.py circle won't bounce off walls

I am trying to get a ball to bounce off of the walls of my bounds. Currently, my circle is supposed to hit the wall and then change velocities and move in the opposite direction but this is not happening. I would appreciate some help :) Thank you

from graphics import*
from random import*
from time import*

win = GraphWin('My Program', 600, 600)
win.setBackground('pink')
my_circle = Circle(Point(200,300),30)
my_circle.setFill('blue')
my_circle.setOutline('darkorchid1')
my_circle.draw(win)

key = win.checkKey()
while key == '':  
    
    vel_x = randint(-30,30)
    vel_y = randint(-30,30)
    my_circle.move(vel_x, vel_y)
    sleep(0.1)
    
    
    for bounce in range(600):
    
        find_center = my_circle.getCenter()
        center_x = find_center.getX()
        center_y = find_center.getY()
        
        if center_x == 600 or center_y == 600:
            vel_x = -randint(30,-30)
            vel_y = -randint(30,-30)
            my_circle.move(vel_x, vel_y)
            sleep(0.1)
    key = win.checkKey()