My First Slip Up

I had my first slip-up yesterday. My future sister-in-law and I went to Barnes and Noble for some free entertainment to read books at the bookstore. However, I was reading this new magazine called "Craft" that just had put out its second issue. I was going on and on about how much I loved this magazine, and as we were getting ready to go, she took the magazine from me and ran to the register and bought it for me. I told her I was going to pay her back (it's a 15 dollar magazine). Anyhow, I am grappling with this slip-up because even though she bought it for me, I want to pay her back. She insists that I don't need to but I can't help myself. I guess in the future I just need to stay out of the bookstore and only go into the library!