just signed a contractor to hire position job

at hourly rate of $40, my currently salary is 73000, since i am laid off and were let go the end of october, that's why i am looking for new job .
At first i thought 73k / year is about $35/hour, so as long as the contractor's rate is a higher than $35, then should be good...

after signed the contract, i figured out i might only be able to commit to work 35 hours/week instead of standard 40 hours/week(due to commute), that adds up to about the same annual salary as i make right now, then i think of i have to deduct the paid holidays and Paid Days offs ...after all that, it's around $8000 less/year than what i make now...

I am a little regret that i sign the contract in a hurry and didn't think about the hourly rate clearly...can i negotiate with higher rate after i aleady signed ?



thanks