Majoring in biology and doing horrible in it?

Do you like the subject? that is the better question. You definitely should do some consideration though. talk it over with some peer advisors (upper classmen) or perhaps TA, Prof, faculty advisors.

No. Decide what you love. If Biology is interesting to you, stay with it. If you think one of your other classes is more interesting, switch to that. Do what you love, it makes studying it A LOT easier. And many schools have "weed-out" classes which, as the colloquialism implies, is like picking the weeds out of grass patches. The 'weeds' are the people who don't really want to be in that major. They don't try and get good grades, and they swap majors because they can't make themselves work harder to pass the class. Now, if you actually like Biology, just look yourself in the mirror and say "I am going to put 50% more time into studying, reading, and getting extra help for Biology. I know that I am capable of getting an A, I just need to put the effort in!" If you love it, you will do just fine. Love conquers all, even in the academic world :)

General biology gave me the most trouble my freshman year, just because there was no real subject focus in it. Once I finished the general biology sequence the other classes felt much better, even though they are harder, there is focus on one subject. Just try your best and finish the general biology, most people (myself included) really enjoy the upper-division courses a lot more. If you love biology stick with it.