Mileage relief for personal Car

I am filling my Self assessment at the moment. I have worked out the amount of money I have been paid for using my car for business, as my company only pay a flat rate of 17p per mile. I put this amount in and it calculated how much reimbursement I would get as tax relief. However I then added a personal pension contribution as well and my total calculation has now gone down from the previous amount. Is this correct?

Hi Stewpot2812,
We would need to access your record to review the calulation. Once you submit your tax return if you allow up to 3 working days to process to our records and the contact HMRC to review Self Assessment: general enquiries.
Thank you.