That's not cylinder #1. Cylinder #1 is the rear bank on the passenger
side. If you must check this, cylinder #4 is up at the same time as
cylinder #1. Cylinder #4 is in the middle of the front bank.
There shouldn't be any reason you'd need to physically check the piston's
location. You can use the timing mark on the crankshaft pulley.
Furthermore, before doing any of that, check your cruise control cable.
If you jacked the engine for access and didn't unbolt the cruise control
module, you probably pulled the cruise cable out of one of the end crimps,
resulting in the throttle being held open.