I guess it depends when you bought the ticket and when you received confirmation of getting *G, because it does take a bit of time for these things to update through the Star network.

You may be able to solve this by going to your booking, deleting your Aeroplan number, saving the change and logging out. Then log back in and re-enter your number. If that doesn't work, you may need to call Aeroplan, since AC won't recognise any *G benefits like lounge access and priority baggage unless it can see evidence that you're qualified for them.