Do yourself justice
Definition 1 of 1
Pro Tip 1/3Context Matters
Often used when someone underperforms despite having the ability to do better. It suggests an opportunity for improvement. 
With better preparation, you will do yourself justice next time.
Pro Tip 2/3Self-Representation
Implying one could have presented themselves more favorably or accurately. 
Prepare thoroughly to do yourself justice during your presentation.
Pro Tip 3/3Emotional Connotation
Carries a slight undertone of regret or motivation depending on the context or tone of voice. 
I felt I didn't do myself justice; I'll aim higher next time.