Why am I starting to look fatter? The other day I did a bunch of exercise, but i look bigger today than then!?

Basically, the exercise I did was 20 minutes cardio, but mostly a bunch of ab and thigh stuff. I was really sore for the first couple of days, and I can tell that I muscle is harder, but when i look in the mirror it seems that my stomach looks bigger. When I feel for the muscle, i can feel it, but only after i feel a bunch of squishy fat. What is wrong with me? Why do I feel squishier and fatter after doing exercises? Is it because the muscle got bigger and made me look fatter or something? WHat do i doo!!???? please help. Im trying to look thinner. THanks.