Without looking at your data, it's impossible to tell what the problem is. As others have said, look very carefully at snapping, visibility and topology issues. Also, simplify your editing environment - get rid of all layers and features to you do not need for this specific edit. If necessary, copy all your 'background' features you want to trace into one layer and use this alone as a standalone single edit.
As John Sobetzer said, you also do not need to complete the entire edit operation in one pass. If you can that's great, if not, you might need to 'build up' the edit using a variety of smaller operations, possibly creating sub-parcels that you can later merge into your final shape.
It's also worth mentioning that there's several ways of killing the proverbial cat without using cream (trace).
If your area is so small, I'd be looking at either overlaying a larger shape and using geometry operations to clip back to the edge you need, or a smaller one and using reshape edge to selected geometry if trace just isn't working..
