Are you shooting for mostly top-middle tier schools? If so, you will need to have a killer application if you want to have a shot applying that late. However, if you just want to go to med school, and you have a good application put together at this point, it can't hurt to try. However, keep in mind that most (if not all) med schools accept MCATs taken as late as September for the following years class. This means that for this cycle, you'll be stuck with whatever you get on the one you're taking this Friday.
I know you originally asked whether or not to take biochem, but as a reapplicant I'm compelled to suggest you wait and apply next year. You'll be able to have everything ready and refined by day 1, you'll know your MCAT and have ample time to re-take if necessary, and you'll have another year of experiences under your belt. Aside from the gap year, depending on how you see it (many find it the best year of their lives to that point), there is no negative to waiting.
In regards to biochem, I say take it. It won't interfere with this cycle if you chose to continue applying, and if you wait, there will be no issue at all. I actually found biochem extremely interesting, which made it relatively easy. And as all the med students have already mentioned, it will help you down the line. I'm personally not a proponent of the "I don't want to do it because it's difficult argument", but in the end the decision is yours.
I hope this helps, and best of luck on your MCAT!
