Most people, I'm afraid, do go through life assuming it's up to them to decide what they'll do with their lives, but I pray you won't be one of them! Instead, I pray you will turn to God and seek His will for your life, because He knows what's best for you.
After all, God made you and put you here; you aren't here by chance. He also gave you your abilities, as well as opportunities to develop and use them. Most of all, He has a plan for your life -- and life's greatest joy comes from knowing His will and doing it. Can you think of any reason not to seek His will? I can't.
How can you find God's will for your life? The Bible tells you what your first step ought to be -- and that is to turn to Jesus Christ in repentance and faith, and commit your life to Him. God loves you; He loves you so much that He wants to come into your life and adopt you into His family forever. Then ask God to guide you -- helping you know your abilities and limitations; opening doors of opportunity for you; showing you by His Spirit what way He wants you to go.
I don't know if you wasted the last four years, but even if you did, don't waste the future! Instead, trust God's promise: "The Lord will guide you always; he will satisfy your needs" (Isaiah 58:11).