1 Samuel 16:7 But the Lord said to Samuel, “Do not look at his appearance or at the height of his stature, because I have rejected him; for God sees not as man sees, for man looks at the outward appearance, but the Lord looks at the heart.”
It doesn't matter how cool you look or how tall you are today — or how uncool you look or how short you are. God's looking at your heart. Get it right via confession and repentance as you prepare to teach or preach God's Word today, and trust Him to work through you.