Having children does change your life. No, you can't do what you want/when, if you have children and that has to be accepted. Of course your relationship changes, it won't be just you and your husband any longer. Your husband will no longer be the centre of your attention, and your child will come before him, especially when very young. You'll both be tired, leisurely lay-ins will be a thing of the past!!
However, as children get older, they become more independent. You don't have to give up your career, you could go back after your maternity leave or stay at home (if finances allow) until your child is say 3, and starts nursery, you then go back to work.
What I will say, is that you and your husband need to be on the same page. Bringing a child into the world, where one person is only going through the motions because of the other person, will end in disaster. You both need to be completely honest with each other. Being nervous about being a parent is normal - I was terrified, once I became pregnant!
I spent most of my adult life not being particularly bothered if I had children or not. I met my husband, we married and had the attitude of 'if children happen, they happen, if the don't, then they don't'. We were relaxed about it. I've never had a raging biological clock. We did decide to have a baby...our son is now 15. I adore being his Mum, and wouldn't change our decision, if I got to choose again. However, if we had decided to not have a child, I'm confident we'd have equally been fine without.