Are you 100% sure that if you died today you would go to heaven?
You must realize and acknowledge the following:
You have sinned
Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:” Romans 5:12
As it is written, There is none righteous, no, not one:” Romans 3:10
“For all have sinned, and come short of the glory of God;” Romans 3:23
There is a penalty for sin: Death, Judgment
“For the wages of sin is death;”Romans 6:23a
"And as it is appointed unto men once to die, but after this the judgment:”Hebrews 9:27
Jesus paid this penalty for you
“But God commendeth his love toward us, in that, while we were yet sinners,
Christ died for us.”Romans 5:8
“For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.”John 3:16
Salvation from the penalty of sin and eternal life is a God's free gift
“...but the gift of God is eternal life through Jesus Christ our Lord.”Romans 6:23b
“And not as it was by one that sinned, so is the gift: for the judgment was by one to condemnation, but the free gift is of many offences unto justification.”Romans 5:16
To have this gift, you simply receive it
“For whosoever shall call upon the name of the Lord shall be saved.” Romans 10:13
“But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name:”Acts 1:8
It's Really That Simple
If you believe what God has to say, then admit to Him in prayer these things:
Confess to God that you are a sinner.
Admit to God that because you are a sinner you deserve His judgment.
Admit to God that you believe that He loves you and that He gave His only Son Jesus Christ to die for you, so that you do not have to spend eternity in hell but you can be in heaven with Him for eternity when you die.
Ask God to forgive you of your sin and to save you.
Assurance
God will keep His promise to you. Here are some verses to help you be assured of your salvation:
“For whosoever shall call upon the name of the Lord shall be saved.”Romans 10:13
For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast.”Ephesians 2:8,9
“He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God.”John 3:18
“And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand. My Father, which gave them me, is greater than all; and no man is able to pluck them out of my Father's hand. I and my Father are one.”John 10:28-30
“...for he hath said, I will never leave thee, nor forsake thee.”Hebrews 13:5b