Geez man, how do you not know you're either failing or in serious danger of failing a course? This is college, you HAVE to stay on top of that stuff - save the "how your grade is determined" stuff from the first week, keep track of your progress, make SURE you get your graded papers and tests back and that nothing went missing, and don't toss anything important til after it's over.
What I would do: talk to the prof, find out what you did wrong. Do not in any way be confrontational, because the prof has incredible powers to help or hurt you - you want HELP. Ask him what you missed or needed to do differently. Ask if it's something you can possibly make up - our school would allow an "Incomplete" with some reasonable excuse, and you turn in your paper or take your test or whatever and then get a real grade. Pull out the "I'm a stupid kid and these were my first courses in college, is there ANYTHING I can do?" if you have to. If it's too late for that, oh well man, suck it up and learn the lesson - PLANNING and MONITORING your progress is pretty damn important to avoid results like this, even worse when they're a surprise. If you're overwhelmed and won't be able to recover, figure it out early enough in the term to be able to drop a course or even two before the cutoff.
On the stress side: what's done is done, worrying won't help now. Count it as a blessing it was only one course and now you learned a lesson, and know what you need to do to keep it from happening again. Your GPA will recover eventually, as long as it's just this one class. And congrats on turning the other grades around, looks like you learned the "Whoa I need to really buckle down and get to work" lesson too, another good one to learn early...