Follicle size before IUI

Dana

Went for my measurement ultrasound today and I've got two follicles measuring at 12mm (one on each side). They are going to scan me again Monday, but what are the chances that either grow to 18mm by Monday?! Can they be smaller than 18 and still want me to trigger? Also nervous I will ovulate before Monday which would be CD 15 for me 😩 so worried this cycle will be canceled :(