If I got your question correctly, then it is unlikely for sp2 C atom to form two pi bonds (C atom makes 4 bonds only: three sigma bonds with N, O, and O "OH2" and one pi bond with O).

Do I understand you correctly that you are wondering why this reaction forms the carbamic acid (A in my scheme) and not the conceivable carboniminic acid (B)?

It's simply a matter of thermodynamics: the carbamic acid is thermodynamically far more stable than the tautomer. Remember that carbonyl groups are among the thermodynamically most stable groups in organic chemistry. Whenever there's a chance to form a C-O double bond (e.g. by tautomerism), the structure will be massively favoured.

Hi Simon, thank you for your explanation.

I'll remember it. Thanks again!

Yes, Simon is correct, notwithstanding that resonance generates a partial C=N double bond and hence partial zwitterionic forms of amides and carbamates.