I may have done this as well... can someone explain to me how to get the sending address, or point me to a thread??

I am looking at the blockchain.info on my TX, but see plenty of addresses, and none saying 'sending address'... I just used an address I knew I could sign with.
I had trouble with this at first as well, this should help:

If you see multiple sending addresses on the left, choose the one in the same row as the amount you sent on the right