I had bleeding 10mths after starting HRT (gel at the time so can't comment on patches). My GP referred me and I was told same as you, thickened lining that needed biopsy just to make sure nothing sinister. Biopsy was all clear so I was able to restart my HRT again. The thickened lining was put down to not enough progesterone and I was offered, and accepted, a Mirena coil which was inserted at the time of the biopsy.
When you get your appt don't be alarmed if it has 'cancer' written all over it. My GP warned me that the appt letter would mention cancer pathway and that it would mention Oncology team on it.
I don't know anything about patches but I'm sure you've probably had more oestrogen than your progesterone prescription can cope with which has led to the thickening.
Hope you don't have to wait too long xx