You are so young, no need to make permanent decision now. Things change over time. I finished when in my mid 30's. I just realized a couple of weeks ago that I definitely DO NOT want any more kids. I love mine, but I am 40 now and looking forward to someday having an empty nest (though my 6 year old tells me he will NEVER move away cause he loves me so much-give him 10 years!))
I wish i would have had them closer together and got each phase over with- I feel like I have started over and over-19, 15, 6. If I would have done it according to plan (hah, people plan, god laughs), I would have 19, 17, 15 and be done with it in a couple of years. I love my kids, and actually thought I would have more. The older ones were great help with the last one though, and he has totally been the light of my life, so maybe plans should be flexible! He is my sunshine. Wouldn't change him for the world. I guess we need to be open to the gifts we get in our children. If I didn't have any one of them, the world wouldn't be as good or as interesting. Though, w/o my oldest, it would be safer to drive!
Short answer: I guess I knew when I had a preg. scare and was TOTALLY relieved that it was a false alarm. Not even a bit disappointed. I was feeling a little off knowing that my days of baby-making were waning, but somehow, it just doesn't seem like a sad thing anymore. It is a new phase in my life to look forward to.