This graph has the shape of a sine function and it does have the correct amplitude. However the period is incorrect. You probably multiplied $\displaystyle{2}\pi\usepackage{cmbright}\Huge\$ by $\displaystyle\frac{{1}}{{2}}\usepackage{cmbright}\Huge\$ instead of dividing. The correct answer is the graph showing one cycle on the interval $\displaystyle{\left[{0},{4}\pi\right]}\usepackage{cmbright}\Huge\$ that passes through the origin.