Please I would want to know: What is the correct pixel dimension for design upload on spreadshirt?
if you create a workspace of 4000 x 4000 pixel minimum then you should create a design within this workspace where at least one dimension reaches the boarder. Or to express it differently: Either the height or the width should be at least 4000 pixels.
I hope this helps.
Upload the two designs and I f the team execpts them both. Then you choose.