If I have to then I will yeah, but it would be so much easier if it just ignored the template when you uploaded it, especially as roblox don’t mention the fact you have to make the template transparent.
The cause of the problem is the grid lines on the clothing template.
Before uploading the template, you should remove all the grid lines like this
There shouldn’t be any visible grid lines on your design.
Simply removing the grid lines doesn’t really fix the problem. Deleting the grid lines will leave visible empty gaps, but it’s a good starting point.
Solution: The way I do it is by using the nearby pixels to cover the grid lines.
This is the same issue I had when I originally made the post.
You need to turn the template layer off before exporting as a PNG, this should get rid of the border lines visible on the character.
It looks like you’ve made your design on the same layer of the template, so I’d advise making the actual shirt design on a different layer underneath the template (so you know what it is supposed to look like on the character) and then disabling the template layer before exporting to PNG. It may look messy and untidy without the template layer but nobody will see it, and I think it will end up looking cleaner on the character. You may have to add the colour you want your shirt to be slightly wider than the templates guidelines to make sure there is no blank space so it wraps properly.
For reference, look at the post made by @CriticalDucky a little further above, with pictures which will hopefully help you!
Let me know if this helps, if not more than happy to talk further!