I accidentally opened the back of an automatic wind unwind point and shoot camera

There is nothing from stopping it rewinding, so either it has rewound until the film is in the cartridge (and without the film start, the camera can no longer resume on its own) or it didn't.

So you can just reopen in the dark and check (but wash your hands and dry them well first). If there is film, taking 3 shots in the dark (and "dark" means dark, like leaving the lens cap on) should get you to a good piece of the negative. If there isn't, without a film start retriever or opening and fiddling with the cartridge in a darkroom (and it has to be completely dark, no emergency light), you won't get anything useful done with the film. And you would need to know how many shots to take before getting to a free part. It would not make a whole lot of sense to take all that risk, for both the sake of photos you already shot and that you are going to shoot afterwards.

I work in a photo lab and can tell you that you lost approximately 5 frames, the one you were on and 2 on either side. If your film didn't rewind then the rest of the roll that was still stored in the canister should b fine. Get it developed since most of the roll should turn out.