To stop a record attempt, enter the race in question and click on the top right button to open the main menu. The first option,"Stop the attempt" will allow you to cancel your current attempt.
A cancelled attempt will not count towards your ranking.
CAUTION: It is impossible to resume a cancelled attempt where you stopped it, even if you accidentally terminated it. The Virtual Regatta team will not be able to help you resume an attempt you cancelled by mistake. You can only start a new attempt.