If you are having doubts, don't marry.
Why not wait for that growth you expect will happen?
In my experience, relationships grow, but don't change. (Not for the better, at least)
In other words, if you have a little tomato plant, you can water and fertilize it and it will grow up into a strong and beautiful tomato plant, but it won't change into a potato. So if you don't want a tomato plant, don't waste your time trying to change it.
If the relationship is great now, it might become even better in the future, sure.
But in all cases where I had nagging doubts about someone's character, or things that slightly annoyed me, I found that those get worse, not better, with closer acquaintance.