You can do everything that you have been called to do. God's grace will be provided for every challenge you face. The greater the challenge, the greater the grace. So, go ahead and face your giant with the confidence that grace will be sufficient to meet your every fear, your every need, and every time you feel like you don't have what it takes. Grace is greater than all your need and all your fear. Trust Him.
But he said to me, “My grace is sufficient for you, for my power is made perfect in weakness.” Therefore I will boast all the more gladly about my weaknesses, so that Christ’s power may rest on me. (2 Corinthians 12:9 NIV)