I'm no guidance counselor or anything close so keep that in mind with what I say here. I took pre-calculus in college and had an instructor with a heavy accent. I could hardly understand her never mind the content of the course. Calculus is really difficult if you don't have any background in it. For myself, I would not want to stay and fail the course. If you are only getting 50's now, and that is with tutoring, I'm not seeing how you can improve within such a short period of time. Keep in mind that, as the course progresses with each passing week, the content only gets MORE difficult. If you feel overwhelmed now, think what it will be like in 4 weeks from now. For me the pressure would be to much with everything else you are dealing with. The little training you've had in calculus has exposed you already. Your certification is important and I would not want to jeopardize that. If it takes you longer to learn calculus so be it. These are just my thoughts. Only you really know what the best decision is here. It will come to you soon if you're not sure now. Best of luck!