That's just the maximum they use to scare people with. Federal sentencing guidelines aren't that severe and a first time offender with something as mild as using the return address to send a few letters would plead out to a few hundred or thousand dollar fine and maybe probation, say nothing of the fact that the OP was underage.

IANAL but to get 20 years they'd have to commit a massive fraud that ended in some serious damage like costing victims million of dollars with some other mitigating circumstances.