Serious Statutory question?

i live in wisconsin and i just turned 18 in oct 08...i ave absolutly no criminal record and im actually leavin for the army this summer when i graduate high school...hopefully...ok i had with a 14 year old freshmen not knowin it was against the law ecause i thought since we were all in high school it was cool...well she lied and said i forced her(as in actually strangling her to have ) and the cops are seein thats not tru so she could face perjury...did not lie to the police and told them that i did not knw i was breakin the law...but i want to knw what are my chancin of goin to jail, probation or a fine, for committin a cl c fenoly with no criminal background and not a bad kid or student...