First ultrasound

Hi everyone when should I schedule my first ultrasound? I was rushed to the ER Thursday because I had the stomach virus, found out I’m pregnant (urine test) BUT when they did ultrasound they couldn’t find anything. I shared with the tech that I’m not even suppose to start till today (Sunday) and she assured me it’s way too soon to see anything. My question is when would they be able to confirm on ultrasound? Should I make my appointment this week or next week? Thank you