Would this do any damage to my car? It is a 3.8 v6 Pontiac Grand Prix.
3/4 of a quart will probably not cause damage, but it may cause some foaming if the crank is dipping into the sump. I wouldn't worry.
You could crack the drain plug and drip out that amount if it bothers you.
i'd recommend checking the level on the dip stick, a little over wont hurt. but ultimately the correct answer is to drain the oil to the correct level.
Disclaimer: I've never tried this myself.
Is it close to being time to change the oil filter? Depending on its position, you should be able to spin it off without losing much more than the oil contained within (which should be ~0.5-0.75 litre). Replace it with a new (empty) one and run the engine for a minute or two then recheck the oil level.
Depending on whether your oil filler tube goes into the block or into an OHV cover, you might be able to syphon off a litre or so through it.