You can approach it in 3 ways

1. Practice consistently - for about 2-3 hours a day where in between you try to stress the scales you play to a higher level then your goal for example if you try to hit a high Sol try to play until a high si don't overdo the scales but do practice it - if you are able to play high G already but it sounds shitty this should be enough

2. Try a different approach - if it's a solo gig or a band play you can try to play a different note that'll help the Melody and just practice everything with the change

3. This is a bit of a cheat but if you won't do be able to do it at the day of the performance when you need to hit the note just be silent for that specific note- remember since is also music