Cement screed height is wrong

[Cement screed height is wrong]

Just to clarify too thick or too thin will crack? I need abt 7mm to 10mm of addition height. 

[Cement screed height is wrong]

My floor contractor say cannot screed anymore as the screed might crack. How true is this? 

[Cement screed height is wrong]

I wanted vinyl flooring for my kitchen, living hall and bedrooms. My cement screed was done at a lower height, shortage abt 7mm - 10mm from my kitchen existing tiles. I was unable to have my vinyl levelled between kitchen and living hall. They have to put on an pvc cap between kitchen and living hall. Is there anyway to fix this? I was expecting the whole flooring to be of the same level.