I would say to listen to your heart and your head. If you are having doubts, then listen to them.
It doesn't get better just because you get married. Being married is hard and stressful, having a family is hard and stressful - you want to make sure you are making these choices with the right person.
I would suggest pre-marriage counseling to talk about some of these issues and other issues that may come up. If he won't go, then that tells you something too.