If you are 17 and your mother is married to a US citizen, you are considered the "child" of a US citizen.
You may or may not be deportable depending on what kind of "papers" were filed for you.
One thing to remember is that if you are contacted by ICE, the Border Patrol, or any USCIS officer, you should refuse to answer their question. Insist on having your own attorney present before you answer questions. Do not answer any questions about whether you have legal status or not.
Traveling in the US near the border with Mexico risks being stopped by the Border Patrol.
What you really need is the advice of a good immigration lawyer. Find one.
Law Office of Lamar Peckham
555 Sebastopol Rd., Ste. C
Santa Rosa, CA 95407
--Admitted to practice immigration law before USCIS, Immigration Courts, the Board of Immigration Appeals, US District Courts, US Circuit Courts of Appeals, the US Supreme Court--
--Practicing criminal defense law in the State of California--
--20 year member of the American Immigration Lawyers Association--
You are considered an "immediate relative" of a US citizen. So your stepfather should immediately file an I-130 petition on your behalf. Whether you are eligible to obtain your green card from within the U.S. will depend on how you entered the U.S. It will be best for you to consult with an immigration attorney.
Best of luck to you.