No you are not entited to redundancy. You chose to leave and will be gone before any redundancy kicks in.
Anyway, is the 90 days really 'a redundancy period' or is it for consultation?
Can you be sure your role will go.
As Kempie says, you could ask your employer to rescind your notice. Or , as a long shot, you could argue that you were ill when you resigned and your state of mind wasn't sound so your employer shouldn't have accepted it,
Finally, can you tell us why you resigned? If you have accepted another job won't you have agreed a start date so you can't hang on.