Solo each track in your project one at a time to see if the met is recorded in any of them.
If not, manually Select each track in the project while holding down the Ctrl button. Each track should become highlighted.
Go to Tracks and choose Bounce To Track(s). For Preset, use What You Hear as a starting point. Source, use Master if your audio tracks are routed through a master bus, or the sound card output if it isn't. Click OK.
Once the mixdown is completed, listen to it to hear if the metronome is in it. If not, export that mixdown.