Your employer an have chosen either to include 'completed' shifts or 'approved' shifts.
Depending on what they have chosen, there are different explanations to why your shift has not been registered in the app:
1) Your employer has chosen 'approved shifts'
In this case you need your manager to approve your shift. The app updates every hour, so within an hour your shift will show up in your app
2) Your employer has chosen 'completed shifts'
In this case you simply need to wait an hour, and the shift should appear within the Butter app.
If not, please check if you shift has been registered correctly in your workforce management system (Planday, SameSystem, Tamigo or other).