Maria, I can understand your concern and believe me, I have been in your shoes. I got a C in the same exact class when I took it in my undergrad career as a Electrical Engineering major, and I am still very successful in my current career as a System Engineer. Getting a C will not preclude you from doing well in your career because you can still come back from that situation. Keep yourself with a positive attitude and think that you are investing in your future now and will be done with this in a few years.
As far as Higher level education, I can tell you that in my opinion, I would actually go ahead and graduate and get a Job with a company that would pay for your Masters Degree. Wait to gain some experience first and then time will determine what expertise you need to go and pursue. This is what I did and I have no regrets. I didn’t pay a penny for my masters degree in System Engineering.