Firstly, knowing you're not cut out for parenthood is a good thing to acknowledge. Too many people don't think it out and the kids suffer. If you aren't sure then don't.
My husband and I have three kids. My wife has four from her first marriage. We all work our asses off to make sure their needs are being met. It is unbelievably hard but we wouldn't change a thing. Love those kids. Love my life.