HELP!Builder built the wrong pool!

We contracted a company to build a 650sqft pool with an additional 80sqft sunshelf. they dugrebar then shot with gunite. My wife and I walked the pool after and we felt something was wrong. It is a freeform design, so I took a string and ran along the "waterline" , then divided by 4 then multipled by itself to get sq footage. The nightmare is true! it is 560 sqft. and our shelf is only 66sqft.

Builder is coming over Monday to walk and measure with his team..... After looking at contract it states he is going to build a 36x18 pool and include a 80sqft sunshelf..... However, there is a sketch that he provided to us, but NOT SIGNED that has pool demensions of 33/17(550). He 100% knows I requested a 650 pool PLUS 80 sunshelf....

It is going to be a very interesting convo on Monday....
Has anyone ever heard of something like this? How much does it cost to hammer out a pool and "redo"?

Love to hear some ideas or advice.
thanks!
for 60K I want the perfect pool