One of the most difficult tasks for a scroll sawer is to match the edges of pieces; whether a 3D cutout or an Intarsia piece. I've found two helpful ways. Most importantly, if you're going to have to match edges, NEVER trace your pattern onto the wood. Make copies of the pattern and attach them to the wood. This ensures that both edges are identical; at least before you cut.
Easiest method: After attaching your pattern, likely with a spray adhesive, cover it with clear packaging tape. The tape will lubricate the blade, cooling it and helping keep it from stretching. Unfortunately, this makes your pattern piece a one-time-only piece.
Most efficient method: Use a product such as Scroll Saw Tape, available from http://scrolleronline.com in 9” by 5' or 9” by 20' rolls. This is a double-sided clear tape that will securely hold your pattern to the wood with no residue. It peels off. This has an added benefit for cutting parts within parts, or adjacent parts, in that you may re-use the cut off pattern piece on the matching piece. It carries the exact line cut for the first piece. For example, I will cut along the lines separating the mice from the cheese, in the photo, and apply the pattern pieces to the wood used for the mice. Easy, peasy.