Sometimes folding salvage to salvage doesn't always line up properly. Next time let the fabric lay where it wants...meaning the salvage edges by not lining up - one side may be at a slope, but the fold will be perfect, then fold again. Lay the fold on the cutting mat lining up the fold with the line, then cut the edge so that it is straight. Sometimes a visual is better so if you don't understand what I'm saying let me know and I'll try to take some pictures and send them along.