(1) If all the work of gas station is of lottery and haram meat then it is not lawful to work there.
(2) Whatever money you have earned from unlawful employment whether they are available with you or spent, you calculate it and give that much amount to poor and needy ones without the intention of reward. If you are unable to pay it once then you may pay it in small instalments as well as keep on doing taubah and istighfar.
Allah knows Best!
Darul Uloom Deoband