Are you 100% sure that if you died today, you will go to heaven?
Realize that everyone is a sinner.
For all have sinned and come short of the glory of God. (Rom. 3:23) No one is good enough to go to Heaven on his own merit. No matter how much good we do, we still fall short.
Realize the penalty for sin.
For the wages of sin is death… (Rom. 6:23) The penalty for sin is eternal death in a place called Hell.
Believe Christ died for you.
But God commendeth His love toward us, in that, while we were yet sinners, Christ died for us. (Rom. 5:8) Christ's great love for us was shown when He died on the cross to pay our debt.
Trust Christ alone as your Savior.
...But the gift of God is eternal life through Jesus Christ our Lord. (Rom. 6:23) For whosoever shall call upon the name of the Lord shall be saved. (Rom. 10:13) Everlasting life is offered to those who, by faith, call upon Jesus.
Now pray and ask Jesus Christ to be your Savior.
"Dear Lord, I know that I am a sinner and that I deserve Hell. I believe that You died for my sins. I ask You to forgive me of my sins and take me to heaven when I die. I am trusting in You alone. Thank you. In Jesus Name, Amen"