hi. Only do it if your sure about it. Use a water based lube which you can get from a chemist, sex shop or sexual health centre. He wont crush you. But if you would be more comfortable in a different position you could try doggy style or the girl on top position where you will have more control. Its normal to feel terrified about sex to begin with. Is there a youth centre that can talk to you about sex and relationships, its its ok to be a virgin but if you really want to take the next step it would be good to get some info about condoms and other contraception. Youth centres sometimes have clinics that are about sexual health. It hurts some people that have sex for the first time because they are not lubricated or relaxed enough. Take longer times on foreplay to begin with. If your not ready its ok don't let anyone force you to to.