Follicles good sized but scheduled for another ultrasound...

I went for my day 11 ultrasound today and saw that I have two mature follicles (24 mm and 15.5 mm). The tech said I would probably get a call later today telling me to take my trigger shot tonight and IUI Wednesday but when they called they said the doctor wants me to come in for another ultrasound and bloodwork Wednesday because they want them to grow a little bigger... I feel like 24 mm is perfect size, no? I’m nervous it’s going to be too big if they keep pushing back the IUI. Anyone experience this??? And have success??