Hello, I'm Keith and happy to help you with your question.
Yes, you do have to file both your self assessment and your PAYE income together on your annual self assessment tax return. It is a pretty straight forward process and you also declare any investment income eg bank or building society deposit accounts interest on the same form. Your tax office will then send you a statement of any additional tax and NI contributions due. If the unpaid tax is under 3K you can have this collected through PAYE by having your tax code number reduced.
I do hope I have helped you with your question.