I forgot my item on cash counter after paying. Can i get my item back I have receipt.

I believe you can get it back. if you ask for a manger and asked that person. Otherwise no.

They can look on a camera and see if you pay for it or not or did someone else pick it up

I can suggest you to see customer service manager or the store manager itself if possible with your original receipt and cash counter number if you remember with the item description ASAP.