Soon as all frames are traced you can go about the meeting points.
I use a No.15 blade which is a curved blade. You can cut with it's broad tip or 'rock it' over the object to be cut.
Just cut the surplus tape at the meeting points which should give you razor sharp angles:

Bit hard to see (too dark, I'm sorry) but the forward edge of the canpy (in the picture on the right side) should give you an idea.
Now you still got to protect the inside. Some people just fit the canopy temporarily on the fuselage. I prefer to spray the canopy and the cockpit sill separately (giives a nicer demarcation on the cockpit sill).
No sprayover must reach the inside of the canopy I'm shure we agree.
So you could simply mask the inside with tape. In the case of my Strike Eagle this is not possible as there's a strengthening bar right across the middle and lots of internal structure.
My approach on this as folows: just seal the 'inside from the outside' as if putting some kitchen foil on a jar (bad example? should read my old literature scool books...).
Well. Pic says more than words:

To make shure the tape sticks only to the underside of the frame (and not up the sides esentially masking what we want to spray) I use this trick:
place a lenght of broad masking tape on some stirofoam sticky side up. Press the canopy lightly onto the tape. Cut round the canopy. For the forward opening repeat the process.