Ultrasound

Today is my first ultrasound! I am about 10w + 4d. Or so I think according to my first doctor. She tracked using my previous period but after thinking about it I think my last period was implantation bleeding so I’m not sure if that changes things and if baby will look bigger than 10 weeks. I know every doctor’s appointment can be different, but what can I expect at this first ultrasound? I have had 1 appointment before at about 4 weeks just to confirm that I am pregnant but not much happened at that appointment and I had to switch OBs. Just curious about previous experiences :) also, how do you calm yourself down from thinking something could be wrong?! TYIA :)