You're practicing your instrument. Good for you! You make a mistake. Not a problem...you're human. But the next issue is: how do you fix this problem?

First of all, go back a few notes to a place before your mistake. Play that section through a couple of times. Are you playing it perfectly now? Then that first mistake was probably just a fluke, and you don't need to read this any further. (But you can if you want to.) If you are still making the same mistake then you need to stop playing and ask yourself a few questions.

What is the problem? Are you out of tune? Is your rhythm off? Does a passage sound sloppy?

Why is there a problem? Are you not hearing the note? Not feeling proper hand placement?

Is there a pattern to the mistakes? Do you keep making the same mistake over and over no matter what you're playing?

The most important thing to ask now is: how do you fix the problem? Now that you have identified what it is, you should be able to go about fixing it and continuing with your practice session.