I know I don't know you and I can't tell how you and your fiance are together. But let me say from your post what I think.
I understand being scared. I think it is completely natural. With that said, there is a LOT of things in your post and, not in your post, that lead me to believe you REALLY need to sit down and talk to your fiance.
First of all, nowhere in the post do you mention that you love him. Do you love him? It sounds more like you are talking about a friend rather than the man you want to spend the rest of your life with.
Second, it sounds like you think that marriage is something that you SHOULD be doing at this point in your life. Yes, other friends your age are probably getting married now and you migt feel like this is the time to do it. However, if you don't have love, passion, or mutual respect for each other, you most likely will not be happy anyway.
You also said that you put pressure on him to get married. You two need to sit down and see if this is something you BOTH really want to do, or if you are just afraid of change, being alone, or losing each other.
I hope you make the decision that is right for you.