Arrested for having pocket knife from WALMART in ILLINOIS?

This cop arrested me because he pulled me over and found a pocket knife in my car. It is isted opening, so not a switchblade. The blade is smaller than the palm of my hand and most likely smaller than 3 inches. I was charged with a cl A misdemeanor and it says ' use of a dangerous weapon'. It also says i 'knowingly and unlawfully had possession of a dangerous knife with the intent to use it'. i absolutely didn't have the intent to use it. I had just purchased it like 3 days earlier. Cop said its not illegal for walmart to sell it, but its illegal for me to possess it. Isn't it a crime as soon as i hand over the money to the clerk then? I am 19 years old. This happened in IL. What may happen to me?