Incorrect. The amplitude is $\displaystyle{\left|-{3}\right|}={3}\usepackage{cmbright}\Huge\$ . You can find the y-coordinate of the high point from this.
The period of this function is $\displaystyle\frac{{{2}\pi}}{{\frac{\pi}{{2}}}}=\frac{{{2}\pi}}{{1}}\cdot\frac{{2}}{\pi}=\frac{{{4}\pi}}{\pi}={4}\usepackage{cmbright}\Huge\$ . You can use this fact, along with the fact that $\displaystyle{y}=-{3}{\sin{{\left(\frac{\pi}{{2}}{x}\right)}}}\usepackage{cmbright}\Huge\$ has a negative sign, to determine where the hills and valleys are. The high point is in the middle of the hill.