Messed up during the Steps to Unlock iphone

I was approved by at&t to unlock my iphone 4s but I accidentally clicked on RESTORE FROM BACK-UP, I didnt want to plug it out because I was afraid it would ruin the phone. Now I already switched carriers to T-Mobile and when I insert the SIM it states SIM not valid. Can I reverse the process, what do i do from here now 😟 ? Please help.