Help! Restricted Cervix?

Hey eve People! Recently I tried having the copper IUD inserted for the first time and for about 45 minutes my nurses tried getting it in. Nothing worked! I had had my uterus measured at the very start of the appointment and my cervix was 'open beautifully' then, but when they tried inserting the IUD it apparently 'clamped up'? We've rebooked to try again in a few weeks and this time they're going to give me a cervix relaxant. It had nothing to do with my muscles being tense apparently, so I was wondering if anyone had gone through something similar, has an explanation or would like to share any tips?