If I dropped off a fake script for pain killers but never went back to get them, can I get into trouble?
There's the legal answer and the practical answer. Legally, yes, you can get in trouble: if you attempt to commit a crime, which you did, you are guilty of a crime even if at some point you got cold feet or returned what was improperly obtained. Practically, if you never went back and your name is not on it, there  is a good chance that the police will not come looking for or find you.