Now I've started to go out further to the side but still trying to maintain my triangular shape. On this type of juncture(90 degrees to one another), it's best to bring the brush tip gradually down to the line width and make your line; then go back and using the very tip of the brush, square up the junction. If you want to square a junction at the end of a stroke, it's better to run a little over and then come back with a DRY paper towel wrapped tightly over your fingernail and rub across the line. If you have solvent in the towel, it is almost impossible to dry the surface to continue painting.

I'm adding a cross line to tie the bottom together. Again I'm working from right to left so I can see where my line is going.