Only when using the sandbox you do not have an acceptance and production environment. So with only the sandbox you have two options:
Both are not ideal, but I would probably go for the second option and take the change that the sandbox can be different.
For the ideal situation you would need a paid license, because then you can go the whole OTAP way.
Regards,
Ronald
[EDIT]
You can reach the backups in the deploy tab and than the tab backup. But I noticed that you can not create a backup yourself. So that makes the second option even further the most logical scenario in my opinion.