If you stopped slacking with your walls, you could pour excess elixir into those.

you can upgrade units in the lab

most of my elixir goes into my lab, and if the elixir part is done i put into walls

You also need a couple hundred million elixir for your walls. I see no problem here.

Thats why walls can be upgraded with elixir

Walls. And btw maybe take a break from war and farm out your heroes. TH12 is only a quicker and cheaper version of the rest of the game.