Please do not listen to your stepfather. He is not telling you the truth. Read the USCIS website. Look for the stepchild iinformation. Your age at your mother's marriage is important.
You can find an immigration law specialist at the AILA. Also, Catholic Charities and Lutheran Relief provide services on immigration issues based on ability to pay. I do see a problem with you being a minor and needing your parent's permission for many things.
A new filing will cost more money than continuing with the current one and will take more time. A K-2 visa, which is how you received your green card, is once of the easiest filings.
It would be best if your father could arrange a meeting with an attorney for you since he appears to be your primary custodian with legal authority over you. An attorney should then have no problem speaking with you.
I do have a question about your stepfather. Is he a naturalized or born US citizen? I am trying to understand why he is giving you incorrect information.

