13 week gender check ?

Is it possible to see what I’m having at 13 weeks ? I’m going to pay (first peak) to get an ultrasound done . I’ll be 14 weeks Monday and having it done Sunday . She said I’ll be fine . Another question , based on my lmp my due date is September 3rd but last ultrasound I had (7weeks) she said based on that my due date is showing sept 8th but she said she’s sticking with the September 3rd for due date . Would that effect my ultrasound as well sunday??