Hold 3-hour retro with actions that must be captured in the next sprints backlog to execute on
A good choice, this is specified in the Scrum Guide as illustrated below
The Scrum Team identifies the most helpful changes to improve its effectiveness. The most impactful improvements are addressed as soon as possible. They may even be added to the Sprint Backlog for the next Sprint.
The Sprint Retrospective concludes the Sprint. It is timeboxed to a maximum of three hours for a one-month Sprint. For shorter Sprints, the event is usually shorter.
This is a good choice and a great way to improve on this choice would be to bring in some data from the sprint to help the team really inspect and adapt upon what has happened previously.
Lets see what other choice could have been made