[A young person has posted about their battle with terminal cancer and their doubt in heaven existing]

Well 1) is why you haven't had success. You lack faith questioning your path like you are. Jesus never lied. You have to have faith all the way for the miracles to happen.
And in the fourth watch of the night Jesus went unto them, walking on the sea. And when the disciples saw him walking on the sea, they were troubled, saying, It is a spirit; and they cried out for fear. But straightway Jesus spake unto them, saying, Be of good cheer; it is I; be not afraid. And Peter answered him and said, Lord, if it be thou, bid me come unto thee on the water. And he said, Come. And when Peter was come down out of the ship, he walked on the water, to go to Jesus. But when he saw the wind boisterous, he was afraid; and beginning to sink, he cried, saying, Lord, save me. And immediately Jesus stretched forth his hand, and caught him, and said unto him, O thou of little faith, wherefore didst thou doubt? And when they were come into the ship, the wind ceased. Then they that were in the ship came and worshipped him, saying, Of a truth thou art the Son of God. (Matthew 14:25-33 KJV)