  We discuss the atom-atom scattering problem across a Feshbach resonance in a
two-dimensional dilute Bose gas at zero temperature, in the limit where the
s-wave scattering length exceeds the width of the vertical confinement. We
determine a tunable coupling-strength parameter and by controlling it we
evaluate how the condensate wave function spreads out with increasing atom-atom
repulsions. We also discuss the stability of the condensate in the
magnetic-field regime where the coupling has become attractive.
