Set a variable to be true when you detect you are inside the circle and false when you detect you are outside. Then in the else condition, you still need to test whether you are still inside the circle, but if you find you are and the flag is already set, don't do anything.
You can adjust this to be a counter instead of true/false, if you want to ignore it for a certain number of times. You can adjust it to be a flag and also a record of the time you bounce()'d it, if you want to check by time.