I got it! Thank you all for your quick replies. I woke up this morning with an idea that actually worked. Traced a template from my EB FG ruler. Used a piece of cardboard to cut a template the size of the end triangle, then trimmed 1/4" seam allowance from the long side. Put the template on the corner of the orange rectangle, then butted up the long side of the fabric triangle. Sewed a quarter inch seam and trimmed the orange fabric. Repeat on the other end. Trim using the EB ruler. It worked!
Again, thank you for your good ideas. It really helps to have people who understand to talk a problem out with.