Hi Misskh
try not to worry, I've been through this several times (and am going through it again).
They're doing precisely the right thing. The gynae may refer you for a biopsy but try not to worry about that, it's just standard procedure.
I assume you're not on HRT other than the vagifem? HRT can cause thickening if the progesterone doesn't balance against the oestrogen properly (which is what keeps happening to me).
Completely get why you're worried, but they have to check you out and likely as not it'll be fine, but that doesn't make it any less stressful