This is extremely unlikely to be anything sinister.
Your endometrium is two MILLIMETRES above the normative value based on women NOT taking any hormonal therapy.
Acceptable limits for women on hormone therapy have not been defined, however some of the most experienced specialists have postulated limits from 8 to 11 millimetres.
Unfortunately the NHS is still working to cutoffs based on a completely hormone starved and atrophic uterus.
Bleeding causes so much unnecessary fear - it is extremely common on HRT because the organ is simply doing what it is intended to do when stimulated by hormones.
Less than 1 percent of endometrial biopsies in women on HRT are pathological, and combined HRT with progestin such as you are on leads to a LOWER risk of endometrial cancer than in untreated women.
However, for peace of mind following your investigations, I would suggest a mirena IUS going forward. This is kryptonite to endometrial cancer - they are even using it to treat early stage endometrial cancer!