If you don't know how to use a global flag, modify your sketch like this:
bool flag = false;
void loop(){
if (flag) {
flag = false;
T2SR();
}
}
ISR(TIMER2_COMPA_vect){
flag = true; }
void T2SR() {
Leave everything before and after this part as is.
When you know more about the timer registers and their coding, you can drop the ISR and check the T2 overflow flag in loop(). I'm too lazy now to figure out which is the COMPA flag and how to clear it.