A pending amount can be a temporary authorization hold for your quoted fare, rather than a completed payment. Your trip payment is finalized after the ride. If you add a tip after the trip has already been paid, it may appear as a separate charge. The time it takes for a released hold to disappear depends on your bank.
If you think you have been charged incorrectly, email support@spinr.ca with the trip date and details of the amount you are querying.