Some details changed as could be identifying.
Say you were 11 weeks pregnant with first baby, scan due thursday but BIL is a sonographer and has their ultrasound machine at home and offers a sneak peak...
Would you?
DP says yes.
I say he isn't at all qualified in this department (pregnancy) and could offer me no reassurance if something didn't look right.
YANBU - don't do it, wait for scan
YABU - Do it!