Yes, you can use heel for that, e.g. heel erg weinig water. Zeer erg doesn't work in the same sense, but both heel erg and zeer erg are used to express something is very bad/severe, e.g. Het ongeval was zeer erg (The accident was very bad/severe).
And also while "very" and "completely" are similar in meaning they are not the same. "The soup is very warm, but it could be warmer." "The soup is completely warm. It can't be warmer or There are no cold patches in it."
I looked for the comment on Wij hebben de soep using Google but it only found this page. How do I find the right comment? If it helps I only use Duolingo on iPad. If there's some special button to click on while doing the exercise, the mobile version doesn't have it.