What can happen if I turn my self in?

My co worker and I were parking at Walmart when we see a cart with a purse. It was both of our ideas to get the purse and search it but I'm the one who got off and got it. She kept the cell phone for herself and I took a credit card. I charged the credit card to a nail salon as $400 gift card. I know have the gift card from the salon of $400 my coworker got rid of the purse. The downfall is that I called the nail salon and she mentioned that I was calling from a dental place (my work) I told her that that wasn't really where I worked that I worked down the street at another place but that we've been getting many calls about problems with our phone lines. I told her my sister was gonna got pick up the gift cards but i went instead and she had no idea I was the girl on the phone. What can happen? Can I get caught? But most IMPORTANTLY will everything be better if I turn my self in? And what is the worst than can happen if I do turn myself in? And I do I go about doing so? I feel so guilt