The posting order runs backwards.
Instagram places the newest post first in the profile grid. To build a continuous 3×3 image, the bottom-right tile must therefore be posted first and the top-left tile last.
The ZIP starts with 01 on the tile you should upload first. You do not have to reverse nine nearly identical filenames yourself.
The grid is a moment, not a locked layout.
New posts move the old tiles. A continuous image is best for a temporary launch or a planned next row, not as a permanent profile structure.
The tool exports portrait 3:4 tiles at 1080 × 1440 pixels, the format Instagram’s profile grid displays today. Choose Fill and crop to cover the whole grid or Show the whole image when empty edges are better than losing part of the subject.