1/4 inch is really not enough to sweat over. Just trim it square and bind it. No one will ever get out a measuring tape to check if one border is 1/4 inch off. Especially if it's the bottom. Since your border quilting runs off the edge on the sides, it won't make a difference if it does on the bottom too.
Did you know that professional photo framers don't use equal amounts top and bottom? They use the same on the sides, but often use a slightly wider width on the bottom than the top. It gives a visual illusion of being equal.