Help with chemistry homework. Equilibrium problem

Question:
For the equilibrium
CO(g) + H2O(g) CO2(g) + H2(g)
the equilibrium constant is 4.0 at 800 K. In an experiment, 1.0 mol of carbon monoxide, 2.0 mol of water vapor, 3.0 mol of carbon dioxide and 4.0 mol of hydrogen gas were introduced into an empty container with a volume of 20.0 dm3 Calculate the concentration of carbon dioxide in the container since equilibrium has been established at 800 K.

I have put up a ICE table and gotten the starting concentrations
[CO]i=0,05
[H2O]i=0,1
[CO2]i=0,15
[H2]i=0,20

I tried putting the concentrations at equilibrium C(eq) as
[CO]=0,05-x
[H2O]=0,10-x
[CO2]=0,15+x
[H2]=0,20+x

Since thats how the equilibrium was written. The equilibrium constant K=4 so:
4,0=(0,15+x)(0,20+x)/(0,05-x)(0,10-x)
And got that x1= 0,3268 x2= - 0,0108
The negative i cant use (?) and the positive one is too big to subtract from my starting concentrations. And when adding the x1 into the equilibrium equation i get K=9,74 so its wrong anyway.

Is there something im missing in equilibrium/acid base reactions/gas reactions/how to work with concentration when different amount of substance of each component is added?