A little scared...

So I'm 19 and in a committed relationship. I've been on BC for a while but I've sucked at taking it at the right time and there are a lot of hormonal side effects that are driving me crazy, so my boyfriend and I finally discussed the IUD option. I'm scheduled for the insertion on Monday and I WAS ready but now I'm reading stories and kinda freaking out... I'm regularly active but have never been pregnant or had kids so I'm wondering if the pain will be worse?? I hear some people can't get it done because of their cervix measurement.... SOS I'm prepared for the worst right now.