You can lay your two colors out on a sheet of glass. Then seam them with a 1/4" overlap right on the glass. Just use the heal of the iron and heat the seam only. Then just put it on as one big piece. Start at the seam and work your way up/down. If your wife is not home, sometimes a large picture from the living room will have glass on the front.
If you get any bleed, trim solvent will take it right off.

David