I think your gut is speaking to you very strongly, and in those times it is so important to listen to it. It sounds like you're not ready now. That doesn't mean you won't be ready in the future. I agree that you aren't your parents and won't necessarily have the same experiences, but a crucial aspect of a committed marriage (or any relationship for that matter) is excellent conflict management and communication skills. It sounds like these weren't modeled to you particularly well as a child. Perhaps you and your DP can get pre-marriage counselling to ensure you have the same expectations and to give you/both of you some tools that you feel you may be lacking?
Good luck with your decision, and you absolutely don't have to go through with it just because you've said yes.