Riddle poem 3

A riddle in a poem, can you find the answer?

You can spin me round

Round and round I go

But I always find my way down

In the middle

Nothingness

Surrounded by hardness

I have but two sides

Sometimes hard to tell which is up and which is down

Part of me reflects, almost like a mirror

Part of me is dull

I’m locked up in plastic

Until someone decides to use me

But my freedom isn’t for long

You can scribe on me

Be it pen or something else

But pencil I deny, and normal ink

Don’t even try!