Those 250k resistors are in the wrong place. They should connect to an opto that provides the zero crossing signal.
Lots of working circuits on Google. Frequency is not really important for the circuit (it is for your programming of course), voltage is for proper current limiting for your zero detector.
Without zero crossing the best you can do is on/off.
That said, if you don't know what you're doing don't mess with line voltages. It can cause fire, explosions, and death by electrocution. There are lots of light dimmer modules out there that you can buy and just connect to your Arduino. Much safer that way (you still have to be careful to not touch the dimmer when in use, best to place it in an enclosure).