The match ends when the ref says so, not when you decide it’s over in your head.

Giving up tends to happen internally, several minutes before the actual finish, and from outside it looks like tiredness. Once the decision is made your body matches it and the result follows. Plenty of games turn in the gap between somebody stopping believing and the whistle going. The clock is the only authority on when it is over.

Agree with yourself beforehand that you will not make that judgement during play, whatever the score. If you catch yourself writing it off, pick one small job and do that until the end. Review the result afterwards, which is when reviewing belongs.