My first "real" quilt had pinwheel blocks. If I could do it, you can too! Just hang in there. I found that I had to play a little with the 1/4" seam allowance because the thickness of the thread affects things when you press the seams.
The Shape Cut slotted rulers were a life saver for me. Like you, I had a really hard time cutting straight lines with a regular ruler - my rotary cutter would go shooting off in all sorts of directions, lol.