The Bible clearly says you can be SURE you will be in Heaven after you die. Eternal life is not something that God gives to you AFTER you die IF He determines you have pleased Him sufficiently. If you are ever going to be in Heaven after you die, you must experience God's 'new birth' before you die.
You must be saved. You must have a personal relationship with God through faith in the Lord Jesus Christ. Without God's salvation you will NEVER be in Heaven.
This section of the website clearly and graphically illustrates how you can be sure of Heaven.