If I am trying to improve and haven't done a lot of sins in a long time, am I still going to hell because I sinned in the past?

No matter how hard we work to improve our behavior, we can never (in heart and actions) be perfect enough to deserve a relationship with God and eternity in heaven with Him. That's why Jesus came: our sins have opened a massive chasm between us and God, and Jesus laid his life down across that chasm so we could be reconnected and cross over from death to life. You need to accept Jesus as your Savior, believing that he died on the cross to save your sins. Once you do that, you have God's forgiveness for all past and future sins. At that point, when he looks at you, God sees perfection because Jesus is in you. You are a new creation.