Should I reject his idea?

My boyfriend and I have been seeing each other for 2 years, and recently he wanted me to sit on his face. I haven't done anything like that before, and I was nervous doing that. We did it after he kept on asking, and I actually hate it, it's so awkward and the thing is, he and I are pretty shy about sex, it's a new territory and this is like the first time he actually suggested something and hasn't backed down from that suggestion, and I don't know if I should tell him to stop, or just pretend to like it.