IVF Stimulation Protocol question

Hi Everyone,

My period started on Saturday(7/29) so I called the clinic today and they gave me the appointment for tomorrow. In this cycle they're gonna do the first IVF. Today is technically my day 3 but the nurse said that today would be my day 2 because the heavy blood flow started on Sunday so Sunday would be my day 1. I am scheduled for blood work and ultrasound tomorrow. This is the first time I am undergoing IVF so can you please help me how this process works? I am afraid that tomorrow would be day 4 and that won't be late to start the stimulation protocol?

Thank you!!