Hi Lauren,
Based on your post, there is a possibility that the upgrade has failed and caused Windows to restore your PC back to its previous version. However, the restoration cannot be completed because the recovery file or the system image for restoration may be corrupted. Hence, an endless restoration loop happens when starting your device.
Having said, we'd like to verify if you have already tried the solution suggested by Jennifer Bri on how to perform a Startup repair. Aside from the Startup repair, you can also try performing a System Restore by following the same steps from the Advanced options.
Once you are done with the initial steps, please respond back with the result so we can provide an additional solution.
We will look forward to your feedback.