You can keep that hide, it doesn't need to be straight sides. It needs to move so he can't use it as a platform to climb out. Corners are especially easy to climb. Once you raise the walls it won't be an issue anymore.
You can use plexiglass (Perspex?) to raise one side so you can see in.
That really is a great enclosure. Well done! But, I would have made a much higher one so as to remain on the safe side: I wouldn't want my tort to climb out without my knowledge. "Better be safe than sorry!"
Thanks for all your advice. I have moved the hide away from the corner and watched him most of the day and he couldn't climb it a it is polished wood and its too slippery. Definitely will raise the sides a well .