i have not took off my cover to look but i got this one ordered locally from this site
JT Sprockets: Motorcycle & ATV Sprockets
it shows the gears ratio's, deminsions for sprockets. i counted 13 spline on the inside. go to the site and check it out. as you described yours aint correct. i ordered mine but the rear is on back order and suppose to get them in 2 weeks. i didnt want to make 2 trips, im in no big rush. you might want to print it out to show them if they are being hard headed. if have delt with autozone and checkers in the past and if there computer say its right even thou its wrong its a hassle to get the right part