Decal Disaster

I wouldn't assign yourself much blame. That doesn't seem like a very well designed decal.

I do think you can work with what's left there. Adding straight lines should not be hard.

For the solid lines get some white decal material and cut to size.  The triangular ones might be a little tougher unless you still have them.  Try to refloat the round one to reposition, but it looks pretty square as is.

Or could he mask and paint the lines in? Just wondering. 

That looks like a tough decal to work with on your first model, as mentioned above.

I have no advice beyond what's already been said to repair it, but maybe a couple ideas to help next time?

Make sure you are applying the decal over a nice shiny gloss coat.

Put a drop of liquid detergent in your waterslide decal tub. This will help keep the water from beading up and creating dry spots when you slide it onto your model. Oh, and use luke-warm water. I don't know why that helps but everybody recommends it and it seems to help.

Maybe try a decal positioning/setting solution like Microset. Sometimes this can bite you, I usually see if I can postion just with the water with drop of detergent first. Don't get confused and use a setting solution like Microsol. The nomenclature is confusing, be careful.

The idea is to give yourself time to gently postion the decal where you want it, especially important with a finicky decal like that one.

Sorry if you already know all that stuff, I have no way of knowing.

Here is an article from FSM 2014 that contains good decal basics, if needed. Scroll about half way down to get to the decal part.

On deck markings like that, the sun UV and oxygen in the air causes them to fade.  You can dial paint flow with an airbrush and overcoat very thinly with the deck color.  Faded decals tend to not show imperfections as much as ones without an overcoat.

Also, for problem decals I put the decal, still on paper, in place, hold a corner and slip the backing paper out.  I put down setting solution first which helps slide the paper out.

Bakster

Or could he mask and paint the lines in? Just wondering. 

 

My thoughts exactly why mess with a decal if you can paint it on.