controls:

acceleration voltage Va

$v_0= \sqrt{2\cdot \frac{e}{m}\cdot V_{\text a}} =$ ${2.652\cdot 10^7}$ $\frac{\text m}{\text s}$

plate voltage Vp

$E=\frac {V_{\text p}}{\text d}=$ ${0}$ $\frac {\text V}{\text m}$

Task:

 The plot of the theoretical trajectory does not always match the trajectory in the experiment.
Test with the experiment, when the differences are particularly visible and conjecture possible reasons therefor.
Real experiment about deflection of electrons in electric field of a plate capacitor
grid for measurement

 y(x) =

$y(x) = \frac{1}{4\cdot d}\cdot \frac {V_{\text p}}{V_{\text a}}\cdot x^2$
Cause for the difference Your opinion Solution
is cause is not cause
not perfect homogenous electric field is cause
influence of the earth' magnetic fiels is not cause
classic instead of relativistic calculation just a litte bit
Influence of gravitation is not cause