IUI finally scheduled

Hello all,
  Just looking for some insight/thoughts here.  Went in for my cd 11 u/s today.  My follicles are 17.5, 16, 15.5, 14, 12, and 12.  They want me to continue on my meds tonight, then take more tomorrow morning...10pm tomorrow night do HCG then go in Sunday at 8:30am for IUI. Now I think that I heard that follicles grow about 2mm a day??? And that they need to be between 15-20 to be mature...just by looking at this does it look like by tomorrow night (hcg) I'll have 4 mature follicles or 6?  I'm just hoping those 12 can catch up but I'm not sure...and do all of the mature follicles release or just the biggest one.  Sorry for all of the questions...I just want this to work! And I'm be okay with twins:):) And today my lining was a 7.5..the said that by the time of the IUI on Sunday it should be around 9 or 10mm.
THANKS!
Shayla