I have a problem with my lip ring? please help me out?

its not that my piercing is infected or anything its just that at the moment i wear a horseshoe lip ring in my lip, and i bought two cones to put on today and now that ive got home and tried to screw them on ive noticed they are just about too big to screw on, is there anything i can do about this? i kno i wont be able to send them back but how can i find out what size my horseshoe is so i dont screw up like this again?