If it is too fast, then your stroke will be too quick.
When you slow your approach to the ball, your stroke will be soooooth.
Using the Golf Metronome will help your body hear a tempo, and your heartbeat will move toward that speed.
Stand behind the ball and listen to the pace of the metronome beat. Approach the putt at that pace. Make practice strokes at that pace. Hit the putt with the same pace.
You will be amazed at how relaxed you will become under pressure and how well you will putt.
Way to GO!