Why is the graph truncated?

Question

I printed the graph as follows, but part of it is cut off.

KleinBottle[a_, b_] := Module[{bx, by, rad, X, Y, Z, u, v},  
bx = 6 Cos[u] (1 + Sin[u]);  by = 16 Sin[u];  
rad = 4 (1 - Cos[u]/2);  
X = If[Pi < u <= 2 Pi, bx + rad Cos[v + Pi], bx + rad Cos[u] Cos[v]];  
Y = If[Pi < u <= 2 Pi, by, by + rad Sin[u] Cos[v]];  
Z = rad Sin[v];  
ParametricPlot3D[{X, Y, Z}, {u, 0, a}, {v, 0, b},    
PlotStyle -> {FaceForm[Red, Red], Opacity[0.5]},   
Axes -> None, Boxed -> False, PlotPoints -> 30, ImageSize -> 600, Mesh -> None]];

KleinBottle[2 Pi, 2 Pi]

Why is the graph truncated?