Paper Tax Return. State Pension started part way through year

I understand that in most cases the amount of state pension received in the tax year is prepopulated. However I am completing a paper return so this will not be the case. I started receiving the state pension part way through the 23/24 tax year and propose simply counting the number of weeks from when I became eligible up to 5 April and multiplying buy my weekly rate. However my last payment was on 15 April so ran into the new tax year. If I do as I propose and the figure does not correspond with what DWP have provided to HMRC will the return be bounced back or will it just be amended by HMRC. Just want to avoid any problems especially as it is so difficult to contact HMRC.

Hi muffin321,
Please contact the Department for Work Pensions (DWP) here:
Contact the Pension Service
To confirm the correct amount of state pension to include in your return.
If the amount entered in your return is significantly different to the figure provided to us by the DWP, we may contact you for clarification. 
Thank you.