It is always best to try and be true to yourself. If you are not happy in a relationship then doing something just to please the other person if it is not what you want can lead to a lot of problems down the line.
At the end of the day if she wants marriage and kids and you don't then it is not going to work as you want different things.
I hope it all works out for you, I am sure it will and in the long run you have done the right thing for hte right reasons.
Lee