Is your lining supposed to be thin or thick during your period? I'm confused on if this is good or bad, what the nurse doing my ultrasound said.

I'm on CD2 the heavy day of my period 😐 and had a baseline ultrasound of my uterus and ovaries today to measure my uterus and measure and count follicles. As the nurse was doing the transvaginal ultrasound she was moving the wand around to look at my ovaries and she said "there's lots of little follicles" and then she started taking pictures of my uterus and measuring it and she went "your lining is thin" I'm not sure if that's good or bad? Is your lining supposed to be thin on your period or what? I'm also starting my first round of letrozole this weekend