Multiple Linear Regression model

Hello All,
I am trying to fit a Multiple Linear Regression Model with 2 predictor variables.

The best-fit parameters returned by pymc3 are significantly different from the true values (taken from the literature).

The data (as a csv) file is here: exp.csv (54.9 KB)

The notebook with the code and a few diagnostic plots can be found here:

What can I do to find a better-fitting model?