Unexpected Result When Using Sinc Interpolation blue is how I tried to sinc interpolate. why would something like this happen?
Since Sinc based Interpolation requires you to know the data at any point it can not be done.

You might do a Truncated Sinc Interpolation.
The artifacts you're seeing can be caused by a kernel which is too short or the parameters aren't good.

In order to create a good Sinc kernel you need to know things about the Band Width of the signal and the Sampling Rate, did you took those into account?