Self Assessment help

I'm a PAYE worker but I sold stock options in July so I think this means I need to become self assessed for the year?
Do I make a return and pay prelim tax by the 31st October?
I paid the tax on the stock options within the 30 days.
Since I'm PAYE and have already paid the tax on the options I'm not sure what prelim tax I'd have to pay?

anyone?

I believe that paying the tax within the 30-days is your full liability and no preliminary tax would be payable and you would not have to register for being self-assessed. A call to Revenue would give you the definitive answer.

Thank you