Beating the last boss and walking off screen to the right will end the game and let you know what your completion % is. So at least you’ll know how close you are :)
SPOILERS BELOW
If you have 100% and beat the boss, wait on that screen for a bit ;P
Have you collected all of the royal bat blood? (Blue blooded bats). My guess is that is the thing you’re missing. It’s a tough challenge, requiring that you avoid damage. Collect them all and return to the bat statue to receive a reward. You can at least fast travel, so plan your route.
If you’ve already done that, feel free to post a pic of the map you have and I can probably point you in the right direction.