This publication should answer ur question.

"R factors in Rietveld analysis: How good is good enough?" Brian H. Toby

The definitions for important Rietveld error indices are defined and discussed. It is shown that while smaller error index values indicate a better fit of a model to the data, wrong models with poor quality data may exhibit smaller values error index values than some superb models with very high quality data. © 2006 International Centre for Diffraction Data. DOI: 10.1154/1.2179804

 I hope if you need a good fitting ( all Parameters) you have to measure XRD more than 3-4 hours and do refinement

the goodness of the fit can be determined from the value of (chi squared, Rf-factor, Bragg Rb factor) where you can consider your fitting is good when the:

X^2

This publication should answer ur question.

"R factors in Rietveld analysis: How good is good enough?" Brian H. Toby

The definitions for important Rietveld error indices are defined and discussed. It is shown that while smaller error index values indicate a better fit of a model to the data, wrong models with poor quality data may exhibit smaller values error index values than some superb models with very high quality data. © 2006 International Centre for Diffraction Data. DOI: 10.1154/1.2179804

@Satish , Sir the scan time was 3 hrs

Delete all atoms and run one cycle refinement, then evaluate backgroud curve fitness.

if you need a good fitting, you should to measure XRD more than 2 hours and then do refinement

Using the Rp and Rwp agreement factors are not satisfactory from a statistical point of view.

For a good fitting: X^2