Sadly, not that I know of... two sides will be straight, but the other two will be zig zaggy. You can cut triangles to fit, or just leave them pointy, or chop off the points to square it up. I've done all three ways on different projects. I like leaving the end points on, so I either make filler triangles to match the border If I'm using a border, or leave the ends pointy if I'm going borderless.
Given how you're building your triangles, I wouldn't cut them off; I would make filler triangles. Fold one of your strip triangles in half, and that is the size your fillers need to be (plus 1/4" on the fold side for seam allowance).