1 Upload
2 Check the crop
Drag a box to move it, drag its corner to resize (the card shape stays locked). With a box selected, arrow keys nudge it (Shift = bigger steps).
3 Layout & download
Page 1 holds the fronts and page 2 the backs.
Print at 100% / Actual size (no “fit to page”), otherwise the card will not be exactly 85.6 × 54 mm.