First monitoring appt today

Samantha • 23yo. TTC #1 for 4 years. PCOS. Blissfully married. Hoping our family is going to start with our first IUI cycle.
Today CD 10 we went to our first ultrasound appointment to check my follicle growth after clomid days 3-7. Unfortunately we only had one follicle on the right side at 12mm and none on the left. The doctor wants it to be at least 18mm. She wants me to come in again on Friday to see how much the follicle has grown in 2 days. They said they should grow 1-2mm per day so I should be ready for the <a href="https://glowing.com/glow-fertility-program">IUI</a> on Monday or Tuesday I am nervous that it won't grow more. 
Have any of you had this issue? Have you had a follicle grow to the appropriate size in a few days for the procedure? We are really sad we only got one follicle to produce. Has anyone had a successful <a href="https://glowing.com/glow-fertility-program">IUI</a> with only one follicle?
Thank you for all of your help and trplies. I am really appreciative.