First IUI Questions

I'm doing IUI with letrozole and a trigger shot this cycle. I went for an ultrasound today and had 6 follicles, but only one is mature (18) I'm going back Friday to see if the others catch up (they range from 10-15) and then possible IUI Saturday. I'm nervous they won't grow enough and my chances of conception will be lower. My nurse said I'm in pretty good shape but would appreciate anyone who could help to ease my nerves! Thank you!