Dave, that wing tip looks pretty good to me. The edges need to be ironed down with HIGH heat.

As for making straight edges over a leading edge or tip, your best friend is a NEW single-edge razor blade. I buy them in bulk packs of one hundred.

Harry Higley makes a gadget for this purpose that uses single edge blades, but it depends on a very sharp blade. Plastic covering dulls blades faster than you would ever believe; if the blade snags during the cutting stroke with the Higley tool, a ragged edge will result.

I have given up trying to make a perfectly straight edge when trimming a color border. I now cheat; I cut a strip of the darker color the necessary width to cover any waves, etc., and iron that down over the seam. Presto; a nice, straight color separation line.

Here's another thing to consider; keep your seams properly oriented. IOW, cover from the bottom up, and from rear to front. That way, the edges of the seams will be pointing "down" and "back" and therefore will not trap fuel residue and/or other crap, nor be susceptible to lifting from the slip stream. The one exception I make here is on wing leading edges. Sometimes you have to have a seam that is "up" instead of "down". No problem; seal it with clear fingernail polish.

In fact, I like to seal all my covering seams with some sort of fuel proofer. I have been using Hobby Poxy clear, brushed on, for this purpose, but my supply is about gone, and irreplaceable thanks to the enviro-nazis. I have tried several other things, without much success. The stuff that works best and most easily (polyurethane) turns a ghastly yellow in short order, especially on white covering. Do NOT use the water-based polyu; it isn't fuel proof, as I found out the hard way.[&o]

Your model is looking great; I'm still trying to find one of those kits.