The short answer is no. See the Catechism of the Catholic Church (all my quotes are from it)
1)Lets say I commit mortal sin (miss Mass on Sunday because I’m feeling lazy; totally screw up at a party and sleep with someone not my spouse; panic at work and forge documents ( btw, I’m just giving examples, not saying Ive done these things!!!)
At that point (assuming you are not sorry), if you know you have done wrong, you are in mortal sin, having turned away from God. Do you go to Hell at this moment for a lapse? I just don’t know, but I would offer prayers for you as I believe you loved God and could be in Purgatory. God’s ways are not ours.
2)I decide to go to confession next Saturday
You have turned towards God so you would be on the right path.
1030 All who die in God’s grace and friendship, but still imperfectly purified, are indeed assured of their eternal salvation; but after death they undergo purification, so as to achieve the holiness necessary to enter the joy of heaven.
3)I have imperfect contrition - I am sorry, but also pretty scared of Hell - I have mixed feelings about my sorrow (as people often do), and I cant claim I have “perfect contrition”.
1031 The Church gives the name Purgatory to this final purification of the elect, which is entirely different from the punishment of the damned.
4)On Wednesday I get knocked down by a bus and killed.
My understanding, because I haven’t made it to confession yet, and my contrition is imperfect, is Im heading straight to Hell - is that right? It doesnt seem right to me, and yet thats the teaching?
1032 This teaching is also based on the practice of prayer for the dead, already mentioned in Sacred Scripture: “Therefore [Judas Maccabeus] made atonement for the dead, that they might be delivered from their sin.”609 From the beginning the Church has honored the memory of the dead and offered prayers in suffrage for them, above all the Eucharistic sacrifice, so that, thus purified, they may attain the beatific vision of God.610 The Church also commends almsgiving, indulgences, and works of penance undertaken on behalf of the dead: (958, 1371, 1479)
Let us help and commemorate them. If Job’s sons were purified by their father’s sacrifice, why would we doubt that our offerings for the dead bring them some consolation? Let us not hesitate to help those who have died and to offer our prayers for them.611
958 Communion with the dead. “In full consciousness of this communion of the whole Mystical Body of Jesus Christ, the Church in its pilgrim members, from the very earliest days of the Christian religion, has honored with great respect the memory of the dead; and ‘because it is a holy and a wholesome thought to pray for the dead that they may be loosed from their sins’ she offers her suffrages for them.”500 Our prayer for them is capable not only of helping them, but also of making their intercession for us effective.
The above isn’t an ideal answer, so I would suggest reading the sections on Purgatory and the Sacrament of Reconciliation in the Catechism of the Catholic Church.