Yes, I found it a pain too to make the lines "line up" and having to check each time on G. Projector, so what I did was create a layer with a simple 100% straight line cutting through the whole image, and then I'd place the straight line where I felt I wanted the two points meet, so I would have a visual guide to know where the lines in both sides had to end to meet in the projection. It made it much easier.