Jagged 3D plot at borders of a triangular domain

My problem is that the 3D plot I am creating appears jagged at the borders of the triangular domain.

I started by creating X,Y coordinates on a square domain. Next, I filtered out the datapoints which lie inside a triangular shape, and called these Xt and Yt. Then I calculated the corresponding function values, and named them Zt.

So now I have Xt and Yt coordinates on a triangular domain and the function values Zt. I have plotted the corresponding graph using the following code:

[qx,qy] = meshgrid(linspace(min(Xt),max(Xt),100),linspace(min(Yt),max(Yt),100);

F = TriScatteredInterp(Xt,Yt,Zt);

qz = F(qx,qy);

surf(qx,qy,qz,'EdgeColor','none')

However, two borders of the plot look very jagged, while one of the borders (the border that is aligned with the straight grid in the XY plane) looks fine.

Can anyone tell me how I can make the two other borders of the plot to appear completely smooth as well?