Multi-track recording I presume?
When tracks are “mixed” together, the waveforms are “added”.
(“Mixing” is sometimes referred to as “summing”).
Usually, when tracks are mixed, the combined mix of tracks is “louder” (higher amplitude) than any of the individual tracks. You can probably see this happen if you look at the playback meter and compare the level of a “solo” track (click the solo button on the track) and the level when playing all tracks together.
See here for more information about the meters: http://manual.audacityteam.org/manual/help/manual/man/meter_toolbar.html
(there are some special case exceptions to this rule, but we can come back to that later if you’re interested. For now let’s just get the wedding CD done 
)
Tip 1
Resize the meter toolbar to full screen width so that you can see it more easily.
Tip 2
If you alter all of the tracks in a mix by the same amount, then the balance of the parts remains the same.
In order to get the mix level down so that it does not distort you can either use the “gain” sliders on the left end of each track, or use the “Amplify” effect.
The advantage of the Amplify effect is that it is very easy to adjust the levels of all tracks by the same amount.
Tip 3
How to select all tracks at the same time: Press Ctrl+A.
Select all of the tracks (Ctrl+A) then select the Amplify effect from the effect menu.
Try setting the “Amplification (dB)” level to -6 (minus 6), then press “OK”.
All of the track waveforms will shrink to half height.
Hopefully this will resolve the distortion problem. If the distortion problem improves but there is still some remaining distortion, or the meters are still hitting 0 dB on the loud parts, reduce the level on all tracks a little more.
Don’t worry if the overall volume level sounds a bit too quiet.
Tip 4
Before exporting the finished masterpiece, save the project (so that you can come back to it if you need to, then,
Select All (Ctrl+A)
“Tracks menu > Mix and Render”
This will mix down all of the tracks into a single track.
Now use the Normalize effect and normalize to -1 dB (minus one).
You are now ready to Export your masterpiece.
If you intend to burn it to CD, export in WAV format.
If you intend to load it into an MP3 player it may still be worth exporting a WAV version as a backup copy before you export as an MP3.
Tip 5
If you wish to save the project again, use “Save As” and give the project a unique file name so that you don’t overwrite the multi-track version.
Tip 6
Don’t delete anything until after the wedding.
Use the “File menu > Check Dependencies” feature before you save your projects to ensure that the projects are self contained. If prompted to “copy in” files, say yes and let Audacity copy them.