How can I be sure I bought the bolt back in right, not in the locked postion. I was sure to install the cam pin into place correctly.

I think I get what you are talking about. When you put the bolt carrier assembly back in the upper the bolt has to be pulled forward, or extended. then slide the handle in where it drops down in the slot and slide in the carrrier with the key in the handle channel then shove them into the upper. I don't think that you can put the cam pin in wrong.  There is really only one way it will go in then turn it 1/4 turn so the firing pin will fit thru the hole.  After everything is assembled always check the function by pulling the charging handle and let it go then pull the trigger (without any ammo in it, of course). You can do this a few times to make sure everything works right.