IMessage crashing after long message Ipad 4

i have a 16Gb IPad 4 IOS 8.1.1 , I sent a really long line of random sentences copied and pasted to one of my friends. Now I whenever I try to open imessage it loads for 10 minutes then crashes to home screen. I've tried turning everything off and on, restarting and waiting. I can't reset or restore because my iPad is for school work, And it's got my teachers Apple ID on it... And restrictions :-( Help please?!