For an IEP, your parents had to have worked with the school to put one in place. You make no mention of your parents--what do they say? As long as you're a minor, they make the decisions. If your parents are unhappy with your IEP, they should hire an education law attorney to deal with the school.
We do not have an attorney-client relationship. I am not your lawyer. The statements I have made do not constitute legal advice. Any statements I have made are based upon the very limited facts you have presented, and under the premise that you will consult with a local attorney. This is not an attempt to solicit business. This disclaimer is in addition to any disclaimers that this website has made. I am only licensed in California.
If you are 18 years old, then you have the right to direct your education (unless your parents have been designated by a Court as your legal guardians because you are incapable of deciding for yourself). Thus,if you choose, you must be part of the IEP team that develops your individual education program.
You may reject all IEP services and request that you be placed in the regular education program, but at your age local state law may prevent you from continuing because you are "too old". The Individuals with Disabilities Education Act (IDEA) requires that services be given to all qualified students until age 21 or upon graduation if sooner.
If you are under 18, which your question suggests, your parents the school can place you in special education through a process that is heavily regulated. If you are unhappy with credit or grades, that can be addressed through your IEP team. Talk to your parents and tell them your concerns. If you are in a situation where that is not an option, speak with a person you trust at the school. Most educators will bend over backwards to address your concerns.