No te preocupes! I speak with a Chilean accent (it's very distinct, and sounds really similar to an Argentinian accent, I've been told) and I had the same concern... I'm not a native speaker, either (it's complicated for me, too,) and switching my pronunciation would be super confusing for me, so I talked to my teacher about it. She's a Spaniard as well as a former AP grader, and told me that accent plays almost 0 role in grading. You can speak however you want--español mexicano, castellano, con yeísmo--and it won't affect your grade. The graders do appreciate hearing an attempt to speak with some
form of a Spanish accent, though, as opposed to a butchered, English-sounding one. The one exception, I guess, would be if your accent was so
strong that it could not be understood by other Spanish speakers...but, from my experience, most people have no trouble understanding my accent.
En resumidas cuentas: ¡cálmate! Sacarás una 5 sin problema