WHS™ and competitions are 2 separate systems and it is important to ensure you pre-register rounds correctly.
General Play:
Best practise for general play is using the MyEG app. The golfer can only download the scorecard at the club and use the app as a digital scorecard. Have the score verified and attested by an appointed person, promptly after play has finished, on the day of play and before leaving the club
If you don't have the app you can still have the more traditional option of registering with the club and returning a physical scorecard before leaving the club.
Competition:
The terms of competition will clarify whether digital technology or a paper scorecard would be used to submit a competition score. Best to speak with the organiser for a copy of the terms.
Duplicated Rounds:
If you pre-register using both the MyEG app, or a score intent has been declared by another method, including the entry to a competition, as the MyEG app is for general play scores only, it will duplicate that round. This means you will only complete one and that will leave an open score which means there is a high chance of you receiving a penalty score or have two identical scores added to your handicap records.