Deep breath. First, you can freak out if you need to, but keep it short and sweet, because now you need to focus on Embryo. Many people that have a tendency to freak out over their grades just choose not to grade their exams until they're all over. I know that's hard to do, but if you're concerned that you're too hung up on biochem to worry about embryo, it may be something for you to think about.
Second, let's put this in perspective. I think roughly 8 people end up having to repeat first year every year. Most of them would very gladly take your C's. You will be able to get a C. Maybe even a B, if you really bust your tail. As far as I recall, class averages tended to go down overall after the first exam, BUT, for those students that didn't do as well on WUME/Exam I, they actually tend to go up because those students make biochem a priority.
It is NOT a big deal if you get a C in this class. I just can't imagine the residency program that would be looking at your app and saying "My god, she'll never be able to be a dermatologist/radiologist/plastic surgeon because she got a C in biochem!". Everyone knows it is one of the least practically applicable classes in med school. Sucking at it doesn't mean you suck as a doctor.
My grades this test block were substantially better than they were first test block. I had a much better idea of what had to be done. Granted, Holliman still handed my butt to me, but in everything else I had a much better understanding of what worked for me, and I was able to get it done.
Unfortunately, TB1 is a much better "practice" than the WUMEs-- it's just very different when you only have one test to worry about that week than when you have them all at once. Some of us are a little slow, and take most of first year to get it together
In my case, I did get a C in gross anatomy and biochem (and I was grateful for both). But I'm still going to be a doctor, and so are you. And neither of us are doomed to family practice
Remember that your first year counts for the least of all of your years of med school. The important thing is that you pass all your classes. If you do better than that, that's fantastic, and you're putting yourself in a great position for some of the ultracompetitive residencies. But by and large, you're going to be just fine as long as you pass.
If you can do better, by all means, you should!! But if you did your best and your best is a C, don't beat yourself up about it. What's really going to matter in the long run are your board scores and your 3rd year clerkships. Hang in there, and go study embryo!!