For a person to say that they are sure of going to Heaven seems like the ultimate in pride and boasting.
If Heaven were something to be earned or won this would be true.
The problem is a misunderstanding about what one must do to go to Heaven.
Eternal life is a free gift.
Jesus' death and shed blood on the cross of Calvary is the basis for the gift of eternal life and it being free.
"This righteousness from God comes through faith in Jesus Christ to all who believe" (Romans 3:20)
"It is the gift of God - not of works, so that no one can boast" (Ephesians 2:8,9)
The penalty for our sin has been paid.
We must recognize our need for Jesus to save us.
We must accept Christ as our savior.
Are you willing to place all of your trust and confidence in Jesus rather than in your own works or effort?
The simple plan of salvation is:
You are a sinner - admit it.
Because you are a sinner you need Jesus.
Just believe on Christ Jesus who was your substitute and died in your place, was buried and was raised again from the dead.
Simply trust God to save you based on what Jesus did already not what you do.
Then take Him at his word and by faith claim salvation.
You say, "Surly that is not all that is necessary to do to be saved." Yes it is absolutely all. It is scriptural. It is God's plan that Jesus would do the saving and we would do the trusting.
Jesus did it all, all to Him we owe.