You have written a session without importing the indexes of the previous session. This can be corrected. If you're not using a CD-RW or Direct CD your data is safe.
When you write a session with CD Creator, an index is built up showing all the files and where they are on the CD.
When you write the next session you should "import" the index from the previous session. Then when you burn, an incremental index of all previous sessions is recorded.
Each time you write a further session you import the previous session, and your current session then lists all files on the CD. On this occasion you didn't do that, but instead wrote a "new volume" without the previous index.
How to correct:
[Read this through and don't do anything until you're confident you can see what we're going to do. Come back here with any questions if you're not happy.]
1) Copy off all the files you can see on the CD back to your hard drive.
2) Run CD Creator in a data project, and with that CD in the burner prepare to add one file (any old file will do)
3) Go to the toolbar, Disc / Import session. You should be shown the sessions already on the CD, and asked which one you want to import.
4) Import the session before the last one you burned. (The last one is the one you just copied back to the hard drive, and the one before that is the one you want.)
This should go get the previous index you lost, and add it to the one file you're about to burn.
5) Burn this latest session. It should be very quick, as it has only one file and the index to burn.
Now, if you eject the CD and then reinsert it you should find that the session you copied off to your hard drive has now disappeared, but the previous stuff has all returned. At this point I would be inclined to copy it off, and then burn a fresh CD with everything on it in one session (session closed but CD left open for further burning).
To prevent this happening again, go to FILE/ CD PROJECT PROPERTIES / GENERAL and check the box for "Automatically import previous session". It's very rare to have a use for not automatically importing the previous session.