You should always query your score at the event within 30 minutes of them being posted if you think it is incorrect. Score sheets can be checked there and then and recalculated if your claim is confirmed. it is free to make a query.
As per the EI Rule Book, Rule 20.1, there is an Objection Form (the Event Secretary will have a copy) which can be filled in and lodged with the Secretary along with €50. As always, the Steward’s decision is final.
If you have left the event before final scores were published and you have a discrepancy, it is unlikely it will be changed. It is your responsibility to check the final results before you leave, or have a friend check them for you.