Assuming you played until right up to the end of the event, it is still possible for your standing to change once all the results are in. The game will tally all players' scores and standings once the event is finished.
This accounting may take some time due to a large number of participants, but you should be able to see the final results in about an hour..
This final tally represents the official confirmed results; some players may find their standing either increased or decreased by a small amount. This is normal for confirming results of tournaments.
Of course, if you stop competing long before the event is over, you could be overtaken by others. It is recommended to continue until events' end to ensure your place.