You need to check the academic policies at your institution. At many schools, if you retake a course, the final grade for that class that will be shown on your transcript will be altered to show the better grade.

Go and talk to an academic advisor or your dean. Be honest about your situation and don't cry or tell a sob story. If something came up during the semester that prevented your from turning in your homework or studying enough (like a sick kid, injured spouse, increased hours at work, etc.) you might be able to ask for an "Incomplete" grade that would give you more time to turn in assigned work. The thing here is that if you need help, you have to ask. The worst thing that anyone will say is "no."

And, if you fail a class, it's not the end of the world. If your other grades are good, one failing grade will not ruin your transcript, especially if you retake the class and get a better grade. If you are already working in your field, future employers may or may not even be interested in your transcript or GPA. They want to see that you've finished the degree.

Either way, show up and take the final. Adult students stand out from the crowd, and professors talk to each other. You don't want to be the student who they remember because she gave up when the going got tough.