If you accidentally created too many entries and the contest is already in progress, what you can do depends on the type of contest.
For self managed contests, contact your contest commissioner and ask them to remove the unwanted entry.
Commissioners can remove the entry by:
Go to the Entrant Manager tab.
Select the member's username.
Locate the unwanted entry.
Select the three dots (⋮) next to the entry.
Select the option to remove or boot the entry from the contest.
Once removed, the unwanted entry will no longer participate in the contest.
For contests that are not self managed, entries generally cannot be withdrawn once the contest is already in progress. Members should always review the number of entries they have before the contest begins and withdraw any unwanted entries while the Withdraw option is still available.