Oh no. As long as semen can find its way inside the girl's vagina she can get pregnant. Doesn't matter if she's entirely naked or have some clothes on. You need to do a lot of homework before you're ready to start having sex.
It depends if semen are applied to any area close to the vagina. Even "pre cum" can be used to impregnate a female. It would be smart if you also put a condom on if your trying to prevent pregnancy.
NO never If you are under 18 u need not know what is going to happen. If by chance plus 18 time to know you got an egg in your womb waiting for sperm of the boy with whom you are dating/sleeping etc...
No it is unlikely reason being the penis had not entered the vagina therefore sperm was not released inside so you cannot get pregnant :) Don't worry! Remember to use a condom.