You asked about whether to use a compass. I have a locking compass, but the difficulty is that I can still hold it at a slightly different angle each time & produce slightly different results. So now I use my compass to figure out roughly where I want my rounded edge & then I use that to create a plastic template (or you can do a cereal box template) and I use that template. Of course, you need to be smarter than I was the first time & think about where your binding is going to end up. Fortunately there are no pictures to serve as evidence of what I did, but I failed to add my 1/4" binding allowance and ended up having to reattach that sliver of my sandwich back onto my quilt. What a mess! I don't think anyone would ever know -- except maybe a quilt judge & fortunately it was neither a competition nor a client piece -- but it was not fun trying to sew that tiny piece back on.