Try not to worry Mojo61. The common side effect of conti patches, for the first six months, is breakthrough or sometimes constant bleeding. If you do have to go for a scan then this isn't anything to really worry about. It will put your mind at rest and, in my experience, isn't a difficult procedure.
If you have a look at the info leaflet you will find that it mentions breakthrough bleeding. I gave up on conti HRT and went back to sequi as, after around eight weeks, I had constant bleeding for six months. Dark blood is old blood. Someone else will be along soon with more knowledge I'm sure.
Taz x