In reply to Lorraine73:
Rhyd Ddu is 895m ascent
Mountain track ascent is 1352m
895/1352 is about two thirds.
So you did two thirds of it in training, which is a decent amount. You will grow some new muscles from that, and I imagine the sense of occasion will spur you on as well on the day. I think you will be fine. Start early and you will have the benefit of long Scottish daylight if you need to take lots of rests. The most important thing I think will be ensuring you have enough water to keep you going but not too much which will weigh you down. You can always pour some out part way if you are obviously not going to drink it all.