I thought it was no longer our option. That the 27 eu countries have to unanimously allow us to remain in the eu now A50 has been actioned.
Don't think it's that clear cut.
To extend A50 beyond March 2019 requires the approval of the EU27 (I think that if push came to shove agreement would be likely).
But there are divided legal opinions on withdrawing the A50 notification and lots of legal folk including the British peer who was involved in writing the clause think that there is nothing to prevent the UK unilaterally revoking that notification.