Sorry, didn't realize you're beneficiary. Now a lot of this makes sense. Still, as an immigrant coming on K-1, there's going to be a period of time when your US citizen fiancé and later spouse will have almost absolute control over your immigration status. You need to ensure they won't stop process due to issues in relationship or financial problems. I'd take time to know your other half as much as you could before committing to this difficult process.
If the lawyer is a real lawyer (searchable on AILA), not a paralegal, then sure, listen to their advice.
Best of luck!