Let me begin this post by saying that I pray all will repent and come to a saving knowledge of Jesus Christ. That being said, I often come upon the misconception that those who are condemned to Hell will wish they had repented and trusted in Jesus. The reality is that they will hate Jesus more than ever and continue to rebel against him.
In Revelation 16 we see this concept repeated three times. As the angels pour out their bowls of wrath on non-believing sinners, demonstrating the power and wrath of God, "they cursed the name of God who had power over these plagues. They did not repent and give him glory" (16:9). This is repeated in verse 11 and verse 21. They curse God for the infliction he brings upon them. They don't wish they had trusted in Him, they hate Him.
Apart from the gracious work of Christ on the cross and the awakening power of the Holy Spirit that opens blind eyes, we would forever be enemies of God. Forever.
Hell will not be full of screams of regret, but of hatred. Their eternal punishment will be just.