Liner replacement size

[Bens33]

I have an above ground oval pool. I need to replace the liner and have a question about the size of the pool. When I purchased the pool the paper work shows it as a 12’ by 21’ by 52” size pool. As I am shopping around online for a liner all of the sites suggest that I measure the pool prior to purchasing the liner to assure a correct fit. I measured my pool several times and the dimensions are 12'7" by 21" by 52". How can my pool be 12.7’ wide? My question is will a 12’ by 21’ overlap liner fit my pool?

Thanks for your help.