Stop! Thief!!

I think I stole gas last night. I went the the station after work because I was on empty. I used what should have been the last $10 in my checking account. So today I'm looking at my online account -which I try to do a few times a week- and the purchase isn't on there!! Then I called my bank and they confirmed that no purchases have been presented to my account.
Now, I'm thinking, what happened? I put the card in once and it didn't go through, so I figured it was a computer error, or because I only had $10 in my account, but the second time it worked so I pumped $10 worth of gas. Was I at the full service pump and didn't realize it? Did I use the pump that you don't need to pay first?
I feel all funky for 2 reasons that contradict each other. I don't condone stealing so I feel like I should say something to the gas station. But on the other hand, if I'd known I was getting free gas I would have probably pumped a full tank. Perplexing.

That is all.