Another axle/hub/wheel question

I just purchased a Dexter axle with 5 1/2" dia hubs from a local distributer. I also got 13" whells and tires cause I wanted a larger tire for a better look. THe 12" tires just looked too small for a 9' trailer. When I tried to mount the 13" wheel it wouldn't sit right and wobbled as it turned. I didn't torque the lugs down but had them tight. I didn't have the wobble with the 12" tires/wheels. When I checked the Dexter cataloge there are tow hubs, a 5 1/2" dia hub for 8"-12" wheels ONLY and a 6 1/2" dia hub for 13"-15" wheels ONLY. I would have thought that since this distributer deals with axles they would have known this. When I called they siad they, the 13" wheel should work. I will go and change out the hubs tomorrow for the RIGHT ones. They didn't seem to think it is a big problem. I think it is. What do you think? Anyone else had this problem? I want it to be right and not to have any problems down the road. (No pun intended!) By the way, this is a great forum and I have learned alot just reading everything here. Thanks for all the great info. 
