"So if Jesus went to hell (I assume before being resurrected?) so we don’t have to, why do people still repent their sins?"
I think you are possibly confusing salvation and repentance.
Repentance is about turning from living a life of sin to living a life that is in accordance with God's revealed will, i.e. a godly life. Someone who is born again has been regenerated by the Holy Spirit, but they still sin every day in thought, word and deed, hence the need to confess our sins to God daily. But for the born again Christian this daily confession of sin is not for the purpose of salvation, because once someone is saved they are always saved, but it is to "keep close accounts" with God, and to walk in close fellowship with Him.
The reason a born-again person needs to repent is because, although the inner man has been regenerated, the corrupt body is not regenerated, the battle with the flesh will continue until they receive a new, glorified body when Christ returns.
Repentance in itself does not save a person, but it is the outworking of the inward work of regeneration done by the Holy Ghost to the soul. I think, going by your question, you are maybe confusing Repentance as a means of salvation.
It is impossible to do anything to "work" your own salvation- Jesus paid it all. If you claim to have faith but your faith amounts to Jesus + (insert: works, prayers, kindness, even faith in itself, charity... the list is endless) your faith then is not resting in Christ, but in something other than Him and His finished work at Calvary. 'My hope is built on nothing less than Jesus blood and righteousness, I dare not trust the sweetest frame but wholly lean on Jesus' name, On Christ the solid Rock I stand, all other ground is sinking sand'.
Either you believe He paid it all or He didn't.
I hope that helps but please ask if anything is unclear.