It looks like you mistakenly chose Stadia as your active save data instead of your Xbox save data. Unfortunately, as you've completed the Cross-Save set up and pressed the final button to activate it, you told the system it was set up as you intended. Once that happened, there's no easy way to switch it out. Before pressing the final button, you could have easily changed it, but not after. At this point, if you want to access your Xbox save data on Stadia, your only option is to disable Cross-Save, wait 90 days, then reenable Cross-Save, making sure to select your Xbox save data as your main save data when you do so. The 90-day wait cannot be avoided or bypassed for disabling Cross-Save.