I've been playing aroubd with an 1997 Canon Sure Shot Owl and I recently put a new roll of film in. The last roll I put in was fine, but after taking 4 or 5 photos the film rewound into the canister as if it was the last on the roll. After I loaded the film, I had a moment where the camera wasn't feeding the film but that was resolved when I pulled the tab slightly further out of the canister and was able to take a few pictures. I know how to fix an accidental rewind, but I'm not sire what to do about those first few exposures without over or double exposing?
If what happened is as you reported, i.e. only 4 frames exposed, you likely will be OK shooting the remainder. This is because the film cassette is light proof thus is protects the yet to be exposed film. Re-load, fire off 6 frames and then shoot.
One can never be quite positive about such things, something might not be as reported. If it were me, I would keep this rolls as sacrificial test roll. You can practice loading and rewinding etc. The decision to use this roll is based on how valuable the images you are about to take are to you.