How to avoid Cusps and Corners when generating spline?

Question

I already asked this in robotics.stackexchange.com, but no reply. So I've decided to ask here

Here I wrote Qubic spline trajectory generation. The following are the result.

Spline that generated

Curvature of the spline

Yaw angle changes

According to Figure 02, there is a sharp change in yaw angle, i.e., between 40 to 45 alone x-axis and the corresponding location of the trajectory is shown in blue in Figure 01.

Question:

Is there a way to overcome such sudden changes when generating spline?