I may not understand. For certain, I don't know what is involved in the statement "went to the wrong calendar".
Anyway, the stock calendar app will show all calendars that are checked in Calendars (see bottom of calendar screen, between Today and Inbox. You should see your Google calendar and iCloud calendar as well as any other calendars. If you check an item there, it will show in the calendar app. If you uncheck it, will be removed from view.
Additionally, if you open a calendar entry and look at the settings for the entry, there is a setting for the calendar associated with that entry. You can use this to move an entry from iCloud to Google, and vice versa. You might manually move your entries if the number of errors is manageable.
As I say, I may have misunderstood, maybe you already know these points. So, for what it's worth.