Hi Pam,
Just wanna confirm here , I believe you are adding the script code to your mbox.js file , if not than try that.
For better debugging of mbox call : can you check the mbox trace by adding the url with the below parameter
?mboxTrace=window&authorization="your-authntication-token"
You can grab the authentication token from your marketing cloud by going to [Target -> Setup Tab -> Implementation on Left Rail ]
Hope this helps .
Regards,
Arpit Gupta