Miter saws are a heck of a lot more accurate that the old radial arm saws but unfortunately most miter saws are not that accurate either. For something like you are doing now, a shop made 45* jig would be in order and incredibly accurate. OK, so much for the future.
Back to your current dilemma. If your mitered corners are not way to much out of whack, you could get a hand saw and saw down the kerf line or make a fancy jig and go down the line with a small router bit. The sawing would make a small gap between the 2 right angle pieces. Use your table saw to make a thin slice of wood (either oak or contrasting wood) and use this slice as a filler. Chisel it flush and finish same at the other pieces. Essentially you are making a decorative plug to accent the joints.
Tony B Retired woodworker, among other things.
"Strive for excellence and settle for completion" Tony B