Being spiritual can mean many things? The question is: what spirit are you looking to for correction, direction, and life? And, what makes you believe the spirit is alive, true, and able to guide you?
Why do you need to be a Christian? Because you need your sins forgiven. There is ample proof to claim that the God of Christianity is the only true Spirit, and only He can deliver you from your sins (Read: How Can We Be Certain the Bible was Inspired by God? How Can I Prove God Exists?)
Heaven and a Hell are real places (Read: Where is Heaven? Is Hell Real? What does the Bible say? Sheol, Hell, Torment, Abyss, Tartarus, Gehenna, Fire, Darkness? What & Where Are They?). Being a spiritual person will not get you into Heaven, but refusing God’s gift of salvation will get you into Hell.
All people have sinned, and all need to be forgiven and made new in order to enter Heaven. God provided the way by giving His Son, Jesus, who took all sin, including yours, upon Himself and paid for them. All you need to do is turn to Him in faith and trust in Him. He will forgive you and give you eternal life in Heaven. No other spirit can do that.
(Read: What If You Die Today?)