Most everyone on this particular forum will have you believe that a 26 is the easiest thing in the world to achieve. Having said that, most people on this forum are of high intelligence, and they aren't really the greatest sample.
It's not easy, but it's not something over which you should shudder. Take the AAMC FL #3 and then you can begin to gauge where you stand. Without any studying, I scored a 23 (6/10/7), and I feel I am your average pre-med student. I am with you on the not feeling too strongly about my pre-reqs. I really feel as if my General Chemistry retention was virtually 25%.
Get a baseline, and then you'll know more. After that, it all depends on how much time you have and how you prepare. Good luck on the practice exam!