The most important thing I can urge you to do is to see yourself the way God sees you. So far in life, you've looked at yourself through the eyes of your parents. Now begin seeing yourself the way God sees you.
How does God see you? He sees you as someone who is very valuable to Him. You were valuable enough for Him to give you life -- but most of all, you were valuable enough for Him to send His only Son into the world to bring you into His family. You are so valuable, in fact, that Jesus Christ willingly gave His life for you. If you had been the only person on earth who needed to be saved, Christ still would have given His life for you. God loves you that much!
God doesn't love us because we're perfect, or because we have it all together (as the expression goes). We aren't perfect, and we don't have it all together! But God loves us anyway -- just as we are. The Bible says, "God demonstrates his own love for us in this: While we were still sinners, Christ died for us" (Romans 5:8).
Confess your sins and your doubts to God. Then ask Jesus Christ to come into your life and begin making you into a new person -- and He will. Then, when feelings of worthlessness try to take over, remind yourself of God's great love for you -- a love that never fades.