Ok, so I know you have until 31st Jan 2020 to complete, submit and pay your self-assessment.
However, my advice gets it in as early as possible.
By now you should have completed your bookkeeping and have everything ready to complete your self-assessment.
So now log on and complete the relevant sections.
Then if you agree with the calculation you can submit.
The good news you know how much you owe, but you don’t need to pay immediately.
You can wait and pay in say November (just place a note in the diary).
This way you are all up to date, you have no chance of fines and you know what you owe.