Hi Nicolette,
Congratulations! Returning to school is a big step, but it's the start of what will undoubtedly be an exciting and rewarding adventure.
I am an adjunct faculty member at a couple of universities, so I, too, am scrambling to get ready for the first day of school (whatever shall I wear?). After doing this for many years, I've finally reconciled myself to the likelihood that I'll never outgrow the back-to-school jitters. I'm as anxious now as I was when I trundled off to school as a child.
I concur with Jane's advice to keep your expectations realistic about what you can do and to be good to yourself. Time and time again I encounter students who are devastated by their grades, in part because they are convinced that every single mark is somehow a determinant of their futures and that every mark below an A+ dooms them to miserable lives of penury and suffering. As you recognize, a student's GPA is only part -- a small part -- of the picture of his or her performance and accomplishments, even for those students who, like you, might be considering further graduate and/or professional studies down the road. But it's easy to get caught up in the pressure to perform at the top of your game all the time.
The advice I often give my students is to aim to do the best you can under the circumstances. Under optimal circumstances, sure, striving for an A might be perfectly realistic; but if, for instance, you're juggling your assignments or exams with family matters, a demanding job, health issues, or the challenges of running an online business, do the best you can with the time and the energy available to you (and as the school year advances, both are inevitably increasingly in short supply), but don't be too hard on yourself if sometimes the work you produce isn't top of the pile. When all is said and done, be sure to reward yourself for all your accomplishments!
I wish you well, Nicolette, as you embark on this new and exciting journey!