  Observation of the cosmic microwave background is consistent with the $R^2$
model. In the $R^2$ model, there exists a dimensionless constant which must be
assigned a very large value to reconcile the model with the data. We show that
the large value for this parameter can be used to propose an extended model.
The scalar spectral index and the tensor-to-scalar ratio of the extended model
have been obtained. Also, we obtain the three-point correlation function of the
curvature perturbation to estimate the primordial non-Gaussianities of the
extended model. It has been shown that the predictions of the extended model
are in agreement with the observations.
