nail it map art

Ehm.. doing it like this (entirely by hand) is basically self-torture. Also anything that isn't flat-shaded is likely going to turn out pretty bad.

Use something like this generator bimbimma.com/minecraftmurals/ instead.
Upload a 128x128 pixel image, set it to only wool blocks, set it to "On ground - top of image is to the NORTH -z", and then create a superflat creative world, make a map, go to the correct corner of the map to set the command block up, and follow the rest of the steps to generate it there. Once that's done edit quirky bits out manually, and then rebuild the result in survival.

Seriously. Spend the time making sure it'll turn out well before going at it in survival. It's worth it.