Is it possible for my dentist to fix what he did to my mouth its way to big after braces the way he expanded my jaw is scaryi didn't get them off yet ?

Talk To Your Ortho: Just talk to your orthodontist, almost everything in othodontics is 'reversible', even some things you may not want to have go in reverse! it may require longer treatment, require select extractions, etc, but it is almost assuredly possible.

Continue treatment: It sounds like you are still in treatment, including palatal expansion. It's not unusual to overexpand and then condense the arch into the desired final form. Continue treatment and ask your dentist/orthodontist if that is what the treatment plan encompassed.

Dentist?: The way your question is stated seems to indicate the dentist (a gp) has been doing the orthodontics. If this is true, it is an often told but sad story. Poorly trained practitioners of orthodontics almost always expand rather than extract teeth and align, close spaces and produce a harmonious bite and profile. If this is true see an orthodontist!

Trust and training: Hopefully you are seeing a fully trained orthodontic specialist. If so, you can trust them to make the correct decision for you. Unfortunately that is not always the case when complex orthodontic treatment is administered by a non-orthodontist with considerably less training and experience. If you're seeing an orthodontist, ask to review your treatment plan. If seeing a gp, go see a pro.