my boat (07′ glastron volvo penta 4.3l) wont shift into gear?

runs, but throttle is stuck- the lever will not move forward or back

Hu… try the throttle/shifter unlock/release button/lever that prevents the shifter to move accidently into fw or rev.
Some have a button on the knob or ring to be lifted before moving the throttle forward or reverse, like most hand shifted cars to go in reverse. (some special handling)
Or…there is something wrong in the throttle box it self.
New boat to you??

1965 glastron boat 17 foot 100 hp mercury out board motor