i turned on my home sharing from my iMac. now the apple tv remote controls my iTunes library. how can i fix this?

There are a couple of ways.

1. You can "Disable remote control infrared receiver" on your computer.

Go to System Preferences, Security, then click on the Advanced button in the lower right.

(note: you might have to put in your password on your computer for this)

Then check the box to Disable the remote control.

2. You can pair a remote to your computer so only that remotes works with the computer.

This way the Apple TV remote will not control the computer.