I stole $20 and kept it for almost two years

This was when I was in grade 6 (12) my teacher would give us change if we brought in over 50 dollars. One day, a kid forgot his lunch money so I took $20 of his change. When he asked me where his money was, I gave it to him, not thinking it was mine. Two years later when I was in grade 8, I was told to pay for a trip and my teacher told me to bring 50 dollars and he’ll give me the change, which was 20 dollars. I brought in 30 dollars and got 10 dollars. I had no clue what the heck was happening. Then I had the realization that I had 20 dollars, I didn’t steal it, I had it for two years, and then I got 10 dollars back. I still have all of it in my wallet.