Since you only have the one Apple ID, you will be fine. If you were to log in you'll have access to all the features available, but you won't be able to sign in with a second Apple ID (besides the one you have) for another 90 days. I think the 90 day wait time is there to prevent music piracy that could happen if your friends came over and simply logged into their iTunes and downloaded all prior music purchases from iTunes in the Cloud to your computer, then you turned around and signed in with your account to upload them to iTunes Match.
Here's a support document about it: http://support.apple.com/kb/ht4627
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Your Apple ID can have up to 10 devices and computers (combined) associated with it. Each computer must also be authorized using the same Apple ID. Once a device or computer is associated with your Apple ID, you cannot associate that device or computer with another Apple ID for 90 days. You can view which devices or computers are currently associated, remove unused devices or computers, and see how long before they can be associated with a different Apple ID from the Account Information page in iTunes on your computer:
- Open iTunes.
- Sign in to your Apple ID by choosing Store > Sign In from the iTunes menu.
- Choose Store > View My Account from the iTunes menu.
- From the Account Information screen, click Manage Devices.
Next to each device or computer name, you will be able to see when each was associated to your Apple ID. You will also be able to track how many days are remaining before your associated devices or computers can be associated to a different Apple ID.
