Is this non-compete enforceable?

I signed a non-compete that seems to state I would be compensated an extra $100 beyond my future compensation for signing but I was never paid such money.

Could this nullify the contact? Could I be paid this at any point during or after my employment to keep the contract valid?

The contract states that by signing it, I agreed I received it. (Which I didn't notice when signing.)

Thank you!

Update:
-I signed it about 1.5 years ago.
-I'd like to develop a webite that either competes against it or is in the same industry but doesn't target the same customers. (It's a niche dating website.) Once my site is ready for launch, I would quit.
-I've kept accurate records of hours worked but I don't have copies of pay checks unfortuately. Hours don't match up to $$$ anyway because he gives arbitrary bonuses based on performance.