Sketch wrapped on curved surface with offset cut

Hi all,

I am trying to cut a channel that loops all the way round the OD of a cylinder. So far, I have created the sketch, wrapped it to the surface, projected the now wrapped sketch back to a plane as a single loop and am now having trouble with the offset cut.

I have used this method for simpler tasks before but not for a sketch that loops the entire way around, is this the problem? I would definitely prefer to have this as one sketch rather that have to try and match them up from either side.

I have attached a few photos for reference (Creo 2.0)

Any help/ alternative methods greatly appreciated.

No3. messy projection & offset failNo1. sketchNo2. wrap