Most amps are not stable at 1 ohm, they are actually better at 4 ohm.
More watts does not directly equal more/better sound. Just means it is even more noticable how crappy it is, just like all the people who roll up with really distorted music and hearing every panel in their car vibrating.
A 500w 4 ohm amp = 2000w at 1 ohm but as stated not many amps are 1 ohm stable.
Its clear you are trying to do this on the cheap otherwise you would have just paid the audio shop to wire all this up who understands ohm loads and parallel vs serial wiring configurations between the sub and amp.
So why dont you tell us what sub you have and we can make a proper suggestion.