I'm still puzzled as to why you are being called for a scan? The 3 monthly long-cycle regime has greatly fallen out of favour, when a trial ( don't ask me to find it!) showed higher incidence of endometrial hyperplasia and maybe endometrial cancer on this regime (if I recall correctly) so docs probably don't want to take the risk. However if you are going to be monitored by the GP or gynae because you are progesterone intolerant then they may sanction this. As sheila says a random scan is meaningless and if you receive a date I would suggest you phone to change the appointment - there is always provision for this if you can't make it, and try to give a date about 7 days after stopping the utrogestan. Even this can be tricky because if you don't bleed or have much to bleed the lining will start to thicken again which is what happened to me - 9 mm on Day 7 or something, though nothing sinister found...
Do preservere if you can - it's honestly the best thing I've done - starting HRT patches late peri-menopause and staying on them ( more or less) for the past 16 years.
Don't despair!
Hurdity x