can sum1 plase tell me,, how did he manage to escape the mutant prison on Three Mile Island???

The pelikula never explained the method, it's doubtful if they ever will for fear of developing even madami plot holes and inaccuracies, and he never escaped a place called 'Three Mile Island' in any other form of media, I'm sorry to disappoint you. It can be assumed, however, from my perspective, that if you were to take into consideration his impressive fighting skills, explosive power, thieving history, and the awesome fact that he is just Gambit, it was difficult but you can imagine how he would have done it just like he did in every other form of X-men media. Does that make any sense? I'm sorry I couldn't be of madami help.