Hi.
It can be tough when you like someone, but find you're not on the same page when it comes to the physical part of the relationship. But consider the most important factor: You don't want to be making out with him.
It's a good idea for you to think about why you haven't been able to say no. Are you afraid you'll lose him? If other girls are doing it, you may feel that you have to make out with him just to keep his interest. My guess is that you will feel a whole lot better setting out your own limits based on what's comfortable for you, and not on what others are doing.
Also, how are you feeling about yourself these days? Having a low opinion of yourself can compound the feeling that you have to do something you don't want to do in order to keep your boyfriend's interest. While there may not be any quick fix to a bad self-image, it is useful to at least understand where your hesitation comes from.
As far as your boyfriend goes, it might help to be clear with him about what you find okay and what you don't. For example, maybe you are fine with kissing, but hate being pawed like a Rottweiler. Or maybe you hate Public Displays of Affection, but are fine making out in private. Let him know your limits.
You might also consider doing more things that involve activities when you go out. That way, you will be less likely to slip into Make-Out Mode. If your boyfriend is not into this idea, it may be an indication that he sees this relationship differently than you do. Would you really feel comfortable being with someone who sees you in such a limited way?
Last by not least, from your letter, I am not even sure how you feel about your boyfriend. Do you really like him or do you just like having a boyfriend? This is an important distinction to consider.