God's Plan (religious warning)

Lately I've been struggling with the concept of God's plan for all of us. As silly as it sounds, this all started when the annoying Jehovah Witness ladies came banging down my door again the other day.These ladies come over and over because I'm too nice to tell them to leave me alone. They're very annoying, and they always seem to pound on our door minutes after we get Christopher to sleep.
Anyways, these ladies came one morning last week, and went through their speech that's typically the same every week. This time was just before Christopher's nap, so I had him in my arms struggling. When I finally said, "if I don't put him down now he'll miss his entire nap" they made to leave. But not before sharing, "just one more thing". They asked if I believed God knew that Adam and Eve were going to sin when he gave them the Garden of Eden. I thought about it and said yes. If God is all knowing, he must have known that they were going to eat the fruit, right? Well apparently I was wrong. (I usually answer wrong when talking to them) And they were quick to point out in their magazine that if God knew that they were going to sin, then he'd be setting them up to fail, which a loving God wouldn't do. They went on to explain how God had a plan for each of us which was free of all sin, and we should try to go as close to that plan as possible, which would give us a life without sin, or near without sin. After the long explanation, I was back to forcing them to leave so that I could put Christopher down for his nap (twenty minutes late, might I add).
Later I got to thinking, though. If God's plan for us really is without sin, then what happens when we do sin? Are we just out of luck? Or does He remake his plan to include whatever sins we commit?
My reasoning for questioning all of this is that I had a lot of plans for myself. I was going to go to a university and graduate, teach while going to school to get my masters and maybe even take some psychology courses so that not only could I teach but possibly be a school counselor. These plans changed dramatically when I got married and had Christopher. I now plan to go to a community college to get my degree. I'll be teaching elementary school instead of junior high music or English. I'll probably never get my masters, or be a school counselor. Honestly, I'm alright with these changes. I took what I had and made it work for me.
What I'm wondering is, will God? If God's plan for me was free of sin, then it wouldn't involve me getting pregnant before we were married. It probably would have been closer to my previous plans for myself. My fear is that once I messed with God's plan, that I failed, game over. Not that I'd suffer forever, but my life would never again be what it was meant to be. What if I was supposed to be a counselor and save someone from a terrible situation? What if, while teaching choir, I reached a student with music the way that my choir teachers reached me? What if my English class was the one that convinced kids that reading wasn't always a bad thing? Even worse, what if, because of my decisions, that terrible situation got the best of someone? What if that kid who just needed a music class, never came out of their shell? What if those kids dropped out because they couldn't pass their English class?
Then again, I could be completely overreacting. Perhaps God does know what sins we will commit ahead of time. Maybe my purpose in life was to marry early and have my children and raise them with all the love that I can and to provide everything that I can for them. I'll never claim to be a religious expert, and in my opinion, even the experts will never know for sure. Proof of that? Ten different religious leaders would most likely give ten different answers. So much of religion is interpretation, that it just leaves me wondering sometimes. Maybe one day I'll know what God's plan for me is, or was. For now, I'm happy with living life the best that I can, and trying my best to be the best mom that I can be.