Is this really stealing?

At school today I went to the local grocery store to buy lunch. After I ate lunch I went to the candy lane where you put your own candy in bags and stuff. I was planning to buy jolly ranchers but I told my friend I would buy him candy aswell. Instead of him getting a different bag to put his separate candy in he took mine and added some recess pieces to it. It was a little amount. I told him I don't think you can do that. Jolly ranchers are more expensive so I took the code of that. Recess pieces are less expensive so I thought it would be better to take the code of the jolly ranchers which cost more per 100 grams. When I went to pay I put the code in the pay your self pal a cashier lady came up to me and told me I'm stealing. I was so scared because I have never stollen in my life. She threatened to call the cops and store security but she let me go. Was I really stealing? I feel really bad