The fact that you are even asking that question shows that you are definately not ready for sex, or any of the risks and consequences that comes with it.
I completely agree with BoyCrazy
when they say, just tell him NO.
Sex isnt about giving in to someone's persistant pleas, just to please them. It is for both of you, and you should only do it when you are completely ready.
Maybe you should try having a conversation with him about it. I dont mean when you are in the middle of making out or anything. Just when the two of you are alone together, tell him how you feel, if youre not ready. It might be a good idea to tell him that you will let him know when you are ready, so he doesnt keep asking/hassling you about it.
Besides, there are a lot of things you can do together that doesnt involve sex.
I hope you manage to sort everything out!