Piece of gasket fell in oil filler cap

If you are really concerned then pull the valve cover on that side and clean it out.

That piece of gasket will float around on the oil when the engine's running. It won't likely interfere with anything, as the only thing it could get into is a valve spring, and those springs are powerful enough that they'd crush any gasket material.

It won't hurt anything. But I'd replace the gasket. Take the cap to your local auto parts store and they can probably match it up. I did exactly that a couple years ago with the gasket on my 03 S10 Pick Up. You can also just replace the cap. I'm sure a new cap will come with a gasket. Hope that helps! Jim