Customising forms on the desktop version is an exercise in patience. The first main problem I'm having: getting the vertical lines to be 90 degrees (not at a slight angle) - it would be so much bett...
What might help is zooming into the form (bottom right corner is the zooming tool). By zooming into the area being worked on makes it much easier to move items and/or design. Zooming in you can actually see what you're doing.
zooming in helps but not very much, especially if the line you're trying to get straight is long and you can't see all of it when you zoom in. If the lines had a "snap to gird" type of feature it would be way better.