Here's my $.02 for what it's worth...
In High school, I struggled through biology, not necessarily because it washard, but it was sooo boring and I HATED IT! Then I took Chemistry, which was MUCH harder, but I really liked it. Think that had to do with being lab partners with my best friend. I finished my first Assoc. Degree in 1996, and had to have two semesters of lab science for it. I took Geology, because it was the easiest. I've never been a science wiz, though I love medical science.
Fast forward to last fall, when I returned to school after 6 years at home with my children. My first class was A&P I. It was HARD, and the teached s*cked!!! It was her first class, ever, and she really wanted to be teaching genetics &/or nutrition, so that's what she taught, but she tested over the book. Go figure! I studied HARD and earned every point of the A that I got. In the Spring, I took micro. It was very hard! The teacher was much better, but there is just so much info covered in such short time. Again, I studied hard, and felt very proud of my B. I can't imagine taking that class in a summer session! I start A&P II next week, and I expect it to be very challenging, too.
My point is, that none of this "science stuff" comes naturally to me, and I'm sure it doesn't to most other people, either. I start the ADN program in August, and I'm sure those classes will be hard, too. But I know I will make a good nurse, and I just focus on that.
Good Luck! I bet you'll do fine!