Was it fair for my employer to terminate me under theft and can it be under another reason less damaging for future hire?

I live in San Marcos, TX. I'm fresh out of high school. Been holding my job for about a year so I'm still green. Well a customer asked me one day how to activate an Xbox card we sell. I was unsure. While I was training, another employee decided to better help customers is to know how a product works. I went through the steps to activate the card. Then once I was done without thinking what I had actually done I put it back on the rack. Went about my shift, glad I knew I would be able to help future customers. Well I came into my shift next day and I was confronted by my manager. Said she would terminate me for theft. I asked why. She said I didn’t pay for the card and asked what I did with the card. I said I didn’t realize that, but I put it back on rack and the cameras could show that. She asked, was I going to pay for the card? I said sure, yeah of course I will, I didn’t realize what I did. I purchased the card. Then she said she had to terminate me for theft. Shaking my head. Is it possible to get my job back from a misunderstanding? I honestly didn’t realize what I had done that day. Any suggestions other than "don’t do that again". I've learned the hard way.