20 week ultrasound question?

In BC , Canada ultrasound techs in hospitals are not allowed to tell you the of the baby. I made an appointment to go to a 3d ultrasound clinic and they can tell you the gender at 20 weeks not any sooner..I may have miscalculated how far along i was when i made the appointment and I would technically only be about 19 weeks 5 days...it might sound silly but does anyone see this being a problem?