If you have filed it already, you have until next January to correct any errors or omissions.
If you have not filed it yet, make sure you do so by midnight on 31 January. After that you will incur a penalty of £100. If you continue to be late, then you might receive daily penalties.
If you are not ready or cannot file your tax return by midnight on 31 January, consider submitted a provisional return with estimated figures. You will have another year in order to submit the final return. That way you avoid any late filing penalties.