From time to time it is a good idea to record your performances or practice sessions. Unless you have studio quality equipment, the tone quality you hear on the recording may not be wonderful, but any recording will pick up timing and relative pitch accurately.
As you listen back to yourself, pay particular attention to areas you think are particularly weak or particularly strong. Anything you think sounds good is worth developing further and anything that doesn’t (e.g., timing, or pitching on high notes) should be the focus of your practice sessions until it is corrected.