This is a rather big region, though much of it is water, so the land size is ok. Do you have plans for the islands surrounding the main island?
The borders shouldn't be simple polygons unless it's due to terrain/infrastructure, here it could make sense to aim for borders that maintain an approximately equal distance from coasts or follow ocean biomes/heightlines. If the borders are just approximate you don't have to change it, we can make them formal later since ocean borders aren't very important to a region's land development.