The Orbit depends on square of velocity and q-factor:
a = -G*M*(1 + q * V²)/(R²)

ax = a*X*(1+q*[Vx2+Vy2])/R;
ay = a*Y*(1+q*[Vx2+Vy2])/R;
Vx = Vx + ax*dt;  Vy = Vy + ay*dt;
X = X + Vx*dt;  Y = Y + Vy*dt;

Start values:
dt = 1.5E-4;  q = 0.005;  X = 0.22; Y = 0;
Vx = 1.6; Vy = 2.0;  ax = 0; ay = 0;

You may change this values!

 

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