Percentage error in time period of a pendulum

The bob of a pendulum is released with an amplitude $\theta = 90^{o}.$ Find the percentage error in the time period of the simple pendulum, if it is calculated by approximating the pendulum to a simple harmonic oscillator.

$\textbf{Assumptions}$

$\rightarrow \text{Length of the pendulum}=2m$

$\rightarrow g=9.8\frac{m}{s^2}$

$\rightarrow\text{Friction and drag forces are absent.}$