I'm not in med school yet, but I thought my perspective might help someone out.
I was an English major (psychology too) and took the bare minimum science classes, except for one biochem course. I graduated in 2004. I went to a small university and have heard that it's not as "good" a school as some of the bigger ones. Whatever that means.
Anyway, I was accepted to a summer medical program this summer. It's a 9-week intensive program designed to give you a glimpse of what first year is like. We did immunology for a week and a half, and then had our final. Then we did microbiology and physiology for three weeks and had those finals. We've been doing biochem all summer, and after midterm we started gross anatomy and histology. To clear that up, we did three classes at a time, dividing the summer in half.
The amount of work was shocking. I mean, you hear about all the studying you should do, but it's not really real until you actually attempt to do it. Sort of like in undergrad, people say you have to study, but I had lots of free time in college even while working two jobs. With little science background, I felt in over my head right away. I've struggled with Biochem, and am just now starting to grasp some of these concepts I didn't get two years ago in my undergrad class. I've had no problem passing (passing is a 60) but I was certainly disappointed by my lack of A's on the tests.
It's hard to just be average. Our class averages usually fall in the 70's. The tests have 16 or 18 questions, so if you just miss a few your grade drops by a lot. But like most things in life, I think it just takes some getting used to. If you've never had to work this hard at school, then you have to adjust and figure out what your strengths are and what the best way for you to study is. Once you get that down you're going to be fine.
I made a 96 on my first anatomy exam last week. It was a great feeling of vindication because I know that I can do the work, even if my grades weren't much more than average. I've got more tests tomorrow so I'm hoping to improve on them as well. If I can do it as an English major, anyone can do it if you have the right attitude and willpower.
Try not to think of everyone else as being more prepared or smarter than you are. Our TAs in the program just finished their first year of med school, and they told us that at least at their school, those with biochem majors were only ahead the first few weeks and then it was a level playing field.
Attitude is important: staying positive helps more than you might think!