Stuck in 1st gear! HELP what happened?

sounds like it's jambed in first. Jack the car up, or at least
the back tires. With the shifter rods unhooked, take a pair of
slip joint pliers. Rotate the tires or driveshaft back and forth
while trying to get both of the shift forks back to neutral.
If you can't, some things jambed in the trans.
If it come out, adjust the shifter and rods to neutral. Try
to install rods and try the shifter. Good luck.