Flush mounted electrical box?

I'm remodeling my basement and installed a half dozen electrical boxes. After putting the drywall up, I realized that one is not flush with the drywall. Instead, it is set back a little bit. I'm able to install the electrical outlet but it is noticeably recessed. Any suggestions of correcting the appearance? In the past, i believe I've seen some type of extension that is designed to sit up against the drywall but I don't know what they're called.