On a song that almost isn't about Harry Potter or much else really

I wrote a song,
and it goes in ursa major
But really,
you can sing it,
to any tune you want.
Like Fred and George,
(or Gred and Forge,
I should say,)
when they chose a funeral hymn,
to sing the school song,
before they needed actual funeral hymns, that is,
(oh, now I made myself sad, )

I wrote a song,
and it goes in ursa major
I played it out loud
(PiOL!)
And now bears show up in my yard
(No milkshake)
I have no clue
where that reference really came from
But I'm too lazy
to look it up.
It might have something
to do with Rebecca Black
I don't know who that is either,
does she have anything to do with
Katy Perry?
Or is she related to Sirius?
(If so should we like her more or less?)
(Because I've noticed that people don't like her
even if I don't know who she is)
(Not that people can't dislike people I don't know...)

I wrote a song,
and it goes in ursa major
the song isn't about much, really,
but then songs are often not
(about much)
Many songs just focus
on rhymes and chords and modulations
While this one doesn't rhyme
and has no modulations
(unless you picked a tune that once was in the Eurovision)
And the rhythm is all **** up
(but I'm hardcore like a rapper)
So this song would be difficult to sing
(Especially to a Eurovision tune)

Besides....
Ursa major isn't a key.