Is it possible to overmarinade a steak?
Yes, the problem will be the vinegar.
Vinegar is acidic and you'll end up with mushy meat. 48 hours is almost certainly too long.  For a vinegar base, I try not to push it over 8 hours and that's only if really necessary. A few hours is typically fine.

Right now, you've got to consider how to save the meat. I'd freeze the meat right now.  Freeze the meat with the marinade (which seems like such a waste for 40'ish hours, but better that than mushy steak). When ready to cook, take it out and let the marinade do its business as it thaws. I'd thaw it in ziplock under running water (quicker than the fridge) and let it marinade a short time and go on the grill. If you let it sit in any unfrozen stage too long, you'll get mushy steak with a vinegar marinade.