Floor leveling - how to?

We went to lay about 96sq m of laminate flooring only to find that the concrete slab is uneven.
I have found a few threads that appear to have had the same problem as us and we gave the Davco self leveling compound a go yesterday, but found after following the manufacturers mixing instructions exactly, we ended up with what looked like a large grey pancake in the middle of the floor.
Isn't this stuff supposed to be of a runny consistency? Enough to allow it to flow to where it is supposed to fill the dips?
We added a bit more water, but found that it had a 'streaky' effect on the top, which according to the mixing instructions indicates too much water and shouldn't be used.
Has anyone used this stuff and it has worked like they claim it should work??
Are we doing something majorly wrong here?
Desperate for advice....