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. Make sure that you are choosing the high point inside the interval [-4, 2].