Nose stud won’t fit

Okay so I got my nose pierced a few months ago. I changed it about two months after getting it because I was getting an MRI and needed to put a plastic retainer in. I changed it back to the original stud right after. It has been about a month since my MRI and I was wanting to change my stud out for a new one. My original stud is a 20g and so I bought the new one in the same size but I can not get the new one in the hole. I can put the original one in and take it out but I can not put the new in. I’m very confused. Any suggestions?