there are a number of circuits online on 555 based "things like this" .. if you are trying to use the 555 to just turn on/off the mosfet (and the load) .. then ... whatever .... but if you are running the 555 at a frequency: a square wave... turning the mosfet on-off-on "khz" times a second , then i like the 555 circuit that uses a few diodes around the pot that is "throttle" (aka duty cycle.. aka the percentage of time the mosfet is on... aka the effective volts the load "sees".... square wave on 50% of the time,,, using 12v batteries, the load "sees" 6v average)
anyway.. the ones without the diodes never turn off 100%..
i think you would be better off with a lm324 instead of a 555 or 556.. ive tried both and the 555 ones all suck... adjusting duty cycle changes frequency etc.. the lm324 was ALOT