Mix of part and full disposals listed shares

I disposed only of listed shares. Some were full and some part disposals. I used the worksheet for full disposals and attached a computation of the part disposals. My tax demand was based only on the worksheet figures so I phoned to say I need to pay more. I was told to amend my return . The only way I could see to do this was by making a new worksheet with just the part disposals proceeds and losses even though this wasn’t strictly the correct format (but the numbers were right). Was there another way to do this?

Hi
Use of the working sheet is not mandatory, so please amend the relevant entries in the 'Listed shares and securities' section of the Capital Gains pages (sa108) to reflect your own overall calculations of the combined part and full listed share disposals