Note:

If you want to paste all pieces into Stitch Painter at once, make your Document size quite large. The width should accommodate the front, back and sleeve widths of the garment plus a bit more, and the height should accommodate the longest height in rows, plus a bit more. Try using a document size of 500 x 500 to start). Make sure that no one piece is selected in the Garment Graphics (pixel-per-stitch) window.