Opened the back of my film camera have I ruined film?

The film could have been spoilt,or you camera has become old.

whats to be confused about , rewinder is broken and your shutter is jammed open anyway , get a new camera , yours is old .

These cameras have an automatic loading system that can be quite finicky.  Not pulling the film out far enough will prevent the camera from loading the film correctly.  A very common mistake users make is to pull the film across the back of the camera too far.  The thinking is that if a little is good, a little more should be better...um...no.  Pulling the film leader too far down into the take-up spool can cause the camera's autoloading system to fail, too.  If, and only if, the film was loaded correctly, the camera will then show a "1" in the LCD.  As you take a shot, the film is pulled out of the canister until there's no more left.  Then the camera will rewind the film back into the can.  Some cameras pull all the film out of the canister and rewind it frame by frame.

The first several inches of the film that was pulled out of the canister when loading is ruined, which is normal.  If after properly loading the film you should open the film door and then close it, the camera will think a new roll of film was loaded and will attempt to advance the film.

You may have just ruined the first few frames.  Don't worry about the film that was still in the canister as it's safe.  If, however, you had taken some shots or your camera pulls all the film out of the canister and rewinds it back frame by frame, then the film on the top of the take-up spool is ruined.  After development, you'd see an area of ruined (i.e. fogged) film, then a few frames where the film was okay, and then another ruined area.

I don't think so.

If I understand you correctly, most of the film was left inside the film canister, and thus wasn't exposed.  So when you reloaded it, maybe you lost your first photo or two, but I doubt that is the case either.

You misloaded the film. If you didn't pull out too much from the canister, it's all right. Just load again, properly this time, making sure you shoot the film's hole in the right place. Make sure you also use a fresh new set of batteries. The first shot may be ruined if it was pulled out that far so put that in mind when shooting.

Assuming the film was still inside the roll (the spool that the film starts out on), that will be safe.  What film was outside of that roll, will have been exposed to light, so that will be useless, my friend.  You CAN still use whatever film was left on the roll by winding your film forward enough exposures to get past those that have been exposed to light.