Keep in mind that BPs LIKE to be cramped. What looks like a tiny enclosure to you is probably nice and snug to them.

A basic rule with tanks is to keep a hatchling in a 10gal until they reach 100g weight. Then, you can move them to a 20gal Long tank (IF they accept it) until they're about 800g, possibly more.

If your snake is hiding most of the day, eating well, and not showing signs of stress then the 10g tank is just right for them. If you move them and they start acting restless, looking for ways out, and not acting normal then they want to go back to the smaller space.
Some snakes like less or more room than others, so you just have to learn your snake. I have two that hate large spaces, and had one a few months ago that just couldn't get enough room.

Get a 20 long, since that would be the next size up, and set it up right. Then see if your snake accepts the extra room. Be sure to have two good hides and plenty of greenery to fill the open space.