Where were you before that address?
If that was your first American address which
you put down on the I-94 when you arrive,
then I don't think you need AR-11 because
you never moved.
If that was not yoru first American address.
Before that you were at other address while
you were on F1, H1B etc, then you should've
used AR-11.
Remember AR-11 is not for PRs. It is for all
non-citizens.
As to whether you should file AR-11 now.
Theoretically speaking, it is too late.