If you let her out when she was in heat, then she will almost definitely be pregnant. I am suprised you did not have all the local un-neutered toms trying to break down your door. The gestation period is on average 65 days. You will be able tell if she is pregnant at about 30 days when you should see a change in the nipples. Pregnant cats also sleep a lot more and also eat a lot more. If you really want to find out if she is pregnant sooner , you will have to take her to the vet.