Mosfet not Switching the current to load

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1) What is the exact type number of your 555? Unless you are using the CMOS variety the 555 output voltage will be about 1.2V below the supply voltage, i.e. will be only about 1.8V.
2) A standard MOSFET needs a gate voltage (Vgs) of about 10V to turn on fully, so with only 1.8V it will not conduct fully. Even a 'logic'level' MOSFET might struggle. What is the rated Vgs(th) threshold turn-on voltage, as per the datasheet, for your particular MOSFET?

 

You are asking about your Mosfet and 555 timer but did not say what is their very important part numbers.

1) Most Mosfets need a gate-source voltage of 10V to fully turn on. Logic level Mosfets need 4.5V to fully turn on. The part number on the datasheet says what it is.
2) An ordinary old design LM555 or NE555 has a minimum supply of 4.5V look at its datasheet, and their output voltage does not go that high. You should be using a more modern Cmos LMC555, TLC555 or ICM7555 that have a minimum supply of 2V, but use a 4.5V supply the same as the logic level Mosfet.

If you need to use your old parts then power the ordinary Mosfet and 555 with a 12V fairly low current supply then use the high current 3V for the load.