Is it illegal?

This is so random... but it feels so wrong so please help me out.

Last week I went to a local store to buy paint. They were having a buy one get one deal on this high end brand! $40 a can!!! Well I was planning on buying two cheap cans for $20 each so I thought, what the hell, same end price for better quality paint.

Went up to the register and it range up $80. I told them about the sign they had up but it was a mail-in-rebate. I HATE mail-in-rebates. Plus, I didn't have $80 ready to spend. Embarrassingly, I had to tell them I couldn't buy it but went and bought two cans of the cheap paint. So I still made a purchase.... just felt guilty that they mixed two cans of the high end paint that I didn't purchase. I was back in the store this week to get home improvement stuff and while there I saw the high end paint I returned (the color I had them mix) for only $10 a can!!! So I bought them. Is that illegal? Because I feel guilty. I felt guilty the whole time. I STILL feel guilty.