Yes, I would start to make a schedule for the certification and work the calculus around that if the calculus doesn't affect anything. The certification affects your ability to work.

Too, you might do a reality check on the calculus; it could be that everyone is doing poorly and that you have a B or C even though you only seem to have scores in the 50s. I know my husband had several courses like that in his undergrad engineering days, and my sister in her nursing school ones.