Abby, I'm so sorry for your loss.
I'm not sure if I understand correctly, but...Jim's feelings of not wanting to go, not wanting to die, don't mean he can't be happy afterwards.
There are stages of dealing with death. Anger and denial are part of that. Generally, we only hear about those who have worked through to acceptance before passing, but it sounds like Jim was not allowed time to reach that point. If we could interview the "souls" who have already passed, we might find many more who admit to fighting to the very end, never accepting what was happening.
I don't believe resisting death has any effect on how we experience Heaven.
However, I can only imagine how much more difficult it is for you to come to terms with Jim's death. And it's only been 3 weeks!
Be kind to yourself, and expect grief to take time to become manageable. God forgives our doubts, fears, insecurity, and anger.