Should I still have a scan!!??

Jo
I'm being tested at the mo for PCOS.. 
I'm due for a internal scan on the 20th April.. Ive heard that you must not have one of these if pregnant as can cause a miscarriage.. ? 
However I am currently ovulating for the first time in 3 months and don't want to hold off trying.. What happens if I catch and i don't show up pregnant before I go for the internal and i actually am 2 weeks!! Very worried.