  We consider the dynamics of a 2D Bose gas with an interaction potential of
the form $N^{2\beta-1}w(N^\beta\cdot)$ for $\beta\in (0,3/2)$. The interaction
may be chosen to be negative and large, leading to the instability regime where
the corresponding focusing cubic nonlinear Schr{\"o}dinger equation (NLS) may
blow up in finite time. We show that to leading order, the $N$-body quantum
dynamics can be effectively described by the NLS prior to the blow-up time.
Moreover, we prove the validity of the Bogoliubov approximation, where the
excitations from the condensate are captured in a norm approximation of the
many-body dynamics.
