Hello to everyone!

I'm new here, as you can see from my date of registration, and I'm new to cartography.

Apologies if my thread is not for here.

Today, I decided to make a map of my own. The thing is, I need it to be enormous.

Its size is 41667 x 41667 with a resolution of 300. I'm following this Photoshop tutorial. Unfortunately, when I use the Difference Cloud + Threshold thing-y + copy/paste the part of coast, the size, compared to my map is quite small and I'll probably need 1000 layers to cover all of my island coasts this way. I was wondering if there's a way to make the parts that I'll be copy/pasting bigger, but with the same resolution. I tried making the "New File" from the first tutorial 30000 x 30000 with resolution 300, but my laptop can't seem to handle it. Any ideas to what I can do about this?