First month if IUI

My husband and I will be doing our first round of <a href="">IUI</a> this month, and I'm definitely anxious/nervous/excited. I am just waiting for the first day of my period so that I can get my prescription for letrozole, then 10 days later I will be getting an ultrasound. I know that all of this is very time sensitive and I want everything to be accurate. I know they told me that the first day of the cycle starts with bright red bleeding, but I've been spotting for two days now, very dark, brownish red (sorry if TMI). I have had significantly more spotting today then I have in previous cycles and I am wondering if today should count as cycle day one because of the amount even though it is not bright red. What are you thoughts on this? I'm sure I'm totally overthinking it, but I'm so anxious about this and of course hopeful that it will work!! Thanks for you help in advance!