A Shopkeeper Who Lost a Check

I made a purchase in a store with a check (without filling in the recipient). The shopkeeper claims that he lost the check and insists that I pay. However, I argue that perhaps someone else will find the check and cash it, and I will lose the money. Therefore, I am not willing to pay. Is my claim justified and why should I pay and put my money at risk?

Shalom!
In principle, you should pay the shopkeeper. However, he needs to provide you with something that will insure you in case the check is cashed by the finder. If he does not provide you with this security, you are exempt from paying.

Pitchei Teshuva, section Choshen Mishpat, chapter