When using transparent glass, whether clear or colored, I set a piece on top of the shape that I will be cutting. I draw a line on the glass over the came where the glass will set in.
Using a glass cutter I score a line into the glass over the ink line I drew out.
I break off the part not needed and repeat with the lower section.
I set the piece into the channel in the came, making sure everything fits and then draw the rest of the shape on the glass. I draw the line to the inside of the shape from where the line is drawn out on the paper because the lines drawn on the paper is the center of the came. If I cut the glass to the exact lines on the design the whole panel would get pushed out and become too large.
Everything fits! Next step is to add the came and work on the next piece.