you could try the backup button, if this does not help you need to start over again if you have not made a backup.

Remember to make a backup regurly, special if you have made a lot of changes, make the backup in step 5 export project.

This is the best fall back in case of trouble.

Hi Andre,

Thanks for the help. Is there no other option? I had only been working on it for one day so it seems a bit bizarre that I should be backing it up so often. Is this a common problem with this software?

Angalee

No it's not a common problem but you are not alone also, it just happens sometimes.
But it is known and there is work being done getting this better. 

But as for all software backup often especially if you have made a lot of changes, it's very easy and fast.
You can also set the build in backup under the pulldown of the save button, x5 makes a small backup at every preview in that case. Still make them also regurly in step 5 export project that's a full backup.

And no there is no other option, so follow steps i layed out and you will be fine.

Not at all, i make backups every few hours but only needed it once over a few years.

And I also test the reliability of the backups - no problems.