Image is lower res after saving to cloud?

Hi guys,

I'm having a kind of weird issue with photoshop. I drew a picture to gift someone for Christmas a few days ago and made it 10 x 10 centimetres big (left all other settings at default). When I drew it, I would frequently go and select View->Original Size just so I could get a feel for how the image would look framed. It didn't look pixelated or low res at all. I saved my work to the cloud as a .psd file.

So today, I went back and opened the file again, thinking I could do a few touchups, but it seems like somehow the size has changed?? It opens at 100%, obviously, which is a tiny thumbnail size now. If I select "Original Size", it increases the zoom percentage to 218% which gives it the right dimensions, but since it's suddenly so zoomed in, the picture is ridiculously pixelated.

Can I fix this somehow? Did I mess up a setting? Or is my only option redrawing the entire thing and hoping this won't happen again ...?

Thanks!