Hello! I'm really new to trading and posted my first offer, ever.
After I got a response from someone, I tried trading with them but I couldn't find the item in my inventory, so I went to try to close the trade and marked it as done.

Now I'm still missing my item and can't do anything to edit the trade.

So a few questions, first: When creating a new trade offer, is it normal to find it missing right after? I didn't trade anyone or do anything else to the item.
Second: What can I do to get my item back if its being held somewhere and cancel the trade offer I posted?

Also, if someone could briefly explain how Tf2outpost works, that'd be great! (Things I should look out for and absolute basics)

Thanks for your help!