When is the earliest you got to see the gender on an ultrasound and was it a boy or girl?

My dr is sending me for a gender ultrasound at 15w 2d, I am worried this will be too early to see the gender and I get charged for each scan. I get another ultrasound at 20 weeks so I am thinking I should just wait for that but I don't know.

Also my dr sent me for dating ultrasound and my due date change which put me at 13 weeks at my last appt but my chart said I was almost 14 weeks, this is weird right? Should I call and make sure this is corrected? Or does it not matter?