If you add to many steps your bank, you have a couple of options:
1. Keep walking but do not add any more distances to your 'bank'; just 'spend' the distances you walk from your 'bank' balance to gradually run down the incorrect distance you 'banked'. This can be useful for small discrepencies.
2. Delete (or undo) the distance via the worldwalking.org website. Please see https://worldwalking.org/help/article/1822/how-do-i-delete-distance-from-my-bank