Too true! Even if he pulled out in time, going back in exposes you to semen still left in his urethra. Early signs of pregnancy might start as soon as next weekend but there is no point in testing until your period shows up light or missing.
Oh yes, that can lead to pregnancy. Unprotected sex even if they do not ejaculate in you is risking pregnancy. The penis emits small amounts of sperm at all times and that is 'enough'. So, you will need to see if you get your period and if you don't, take a test. It's not a huge risk but a risk. Get some condoms or go on the pill so you don't have to worry about this in the future. You can test 2.5 weeks after it happened. good luck