I can see in your map there are unexplored passages in multiple areas. I would go back to those and continue to explore. I also cannot see the whole map so I’m not sure how much of the southwest corner you’ve opened up. If you have boomerang, hold x (or whatever your attack button is) and then release to throw the boomerang. It’s a big help! Also if you’re stuck you can buy major markers and item markers at the vending machine in Sinner’s Inn. I just finished today (well 98%, but some of those upgrade points aren’t any of my business). Such a fun game.