Anatomy and Physiology I (now the real fun begins!)

Recently I completed developmental psychology (my second completed prerequisite course) and I am happy to report that I got an 'A'! I certainly am on the right track but developmental psychology is still, for lack of a better phrase, not a "hard" science like Anatomy and Physiology, Microbiology, or Chemistry, which are the bulk of my prerequisite courses. I of course took life sciences in the past; I am even a little familiar with anatomy and physiology from my CNA training back in high school and I recall enjoying the subject material but that was well over 15 years ago and I did not get an 'A' in that course (I believe it was B+) or in any other life science course for that matter. To even be considered for admission to any nursing program I should be getting 'A's in the majority (if not all) of my courses. I was also a science major with my first undergraduate degree (computer science) but rarely got an 'A' in my courses (in my defense my major courses were primarily boring). I am certainly one for a challenge (I even secretly like them at times) but I am nervous about my potential performance in Anatomy and Physiology I especially since its all online. I do not have the luxury, time, or money to repeat any of my courses and many nursing programs, include those I am interested in, will not accept repeated science courses.  As the precursor to all of the other sciences I have remaining, this course could essentially make or break me! I am a better student now in my 30s than I was in my late teens or early 20s but I have a pretty busy life and the occasional attention span of a peanut. And although I generally work well under pressure I am a ticking time bomb on the rare occasion I become overwhelmed. Am I being a little dramatic? Probably. But the competition is fierce and in the Spring 2014 semester I will truly have to bring my 'A' game.