What do I say back to him...?

Don't stress, and don't do what you feel uncomfortable about doing. This is very cliche, and I usually hate the saying, but it applies here, when the time is right, it will feel right. Statistically speaking a lot of girls have for the first time against their will, and it causes a lot of the same problems and inhibitions about that you seem to be experiencing. Maybe try talking this out with the guy and see if he can start slow with making out and work up once you feel ready. Best of luck.