I've always found Paint to be the easiest way to shrink drawings into the template. Just open the template file in Paint the copy paste your drawing and you can then shrink it down exactly into the template. It has to be touching the edges of the inner line but not overlapping by a single pixel.

Old school but pretty easy to do!

Clip studio paint? Does it still run?

Paint in Windows is what I've always used. I drew my pics in other programs, saved them then superimposed them over the template open in Paint and stretched them so they sat perfectly within the template. Then saved that file to upload via Black Pearl.

You may be able to do this in your own software, I'm sorry I'm not familiar with Procreate.

The problem is if you change the size or shape of the template even 1 pixel or if your drawing overlaps the template in anyway/does not sit exactly next to the line of the template then you will not be able to upload it. It will tell you there is an error when you try. If you want a larger canvas it's very difficult/impossible to draw it within the template straight away.

Oh that's crazy about lining it up to the pixel. Do all edges need to touch or just one edge?

I found each inside edge of the square/rectangle has to touch your drawing but not overlap or it says no! With Paint you can zoom in on each edge and just drag it upto the line.

It may be worth keeping this open for a bit in case you get other ideas/strategies from other players who may be more technologically adept than me!

Thank you for this. Do you know if the dimensions are a perfect square?