Last night I finally finished the pattern.
I took Anita's suggestion and removed some excess from the side by allowing the edge to go straight rather than gather up. I ensured that the top line measurement is still the same, so the waist should fit but the gather is slightly reduced. I'm confident now I can gather that much into the side but I will have to gather the fabric tightly.
I drafted up the skirt portion with the waterfall front slit. I've only drafted up one side because they will both be identical, with a plan to just flip the piece over when cutting out because it's so bulky and annoying! I can chalk in the bottom line to keep it level.
Next concern: I realised that cutting the skirt with the stretch horizontal (so across the hips) probably isn't going to give a nice waterfall drape. I think to get the drape I'm going to have to cut it the other way. I need to test out how the drape hangs. There is a possibility that I won't be able to get the waterfall to work. If this is the case, I will just cut it off and have a flat slit instead. Running out of time to worry about it!
I've got Wednesday off so I can work on it then. Also got the top to make, but as a last resort I can just wear a black top with the gold skirt (my theme colour is gold, so I have to have something gold on!)
Hoping to cut the skirt tonight