Need help

Hello people,
I lost my beloved dad in June this year after a short but intense sickness. He was the healthiest man in town with no co morbidities or any lifestyle related ill habits. In Feb this year he was diagnosed with aggressive brain cancer and by June he left us. He was 68 and in perfectly fine shape.
The issue I am facing and probably need help with is, that I am unable to make sense of anything. I am lost, I am angry, I am devastated and helpless. I am unable to come in terms with the finality of death. We had some difficult and incomplete conversations last year and I really really thought I had all time in the world to get him on my side but guess fate had other plans.
I grieve not just for his passing away without any prior history of diseases but also because we had to patch up and be the best dad daughter duo as we were for last 29 years.
I feel I hurt him immensely during last year without ever thinking I might never have the time to make up for it. Honestly, self harm is the only way I see to get over this feeling and meet him up there for our incomplete conversations and to express my love to him.
I am sorry but what do I do. Please help if anyone has ever faced such a situation. Thanks.