I'm trying to burn to CD

How do I put multiple tracks on CD from Garageband? I have managed to burn one track, but how do I put more on? Every time I try it says:

The disk you have inserted is not blank. Please use a blank CD-R or CD-RW disk.

It's not blank because I've already burned one track! Can someone please help?

Hello again! I have just gone through the whole process which somebody very kindly sent the link to, and still, at the end of it, it tells me that I do not have a blank CD, therefore it will not add to the track that I have already on there. This is rather frustrating...I realise that I must be doing something wrong, but I really am at a loss. My CD is CD-RW.
ANy other suggestions will be gratefully received...

The link itself is perfectly clear in its directions, so I can only assume that you're not following them carefully.

Macs don't do "multi-session" burns (not without special third-party software, anyway). So you can only burn ONCE. That is why the link above says to bounce your songs to iTunes, make a playlist of all of them and burn it then.

In other words, if you have anything already on the disc, this won't work. You must erase the CD-RW (not quick erase) or use a blank CD-R.