Health coverage questions after I get a job this year

I was "let go" from my job last November. I signed up for health coverage in March. I recently started a new job and will be able to receive health coverage starting in September. Between my wife and my income, it could possibly put us over the limit on the premium tax credit. Will what I earn in the second half of the year be prorated against the first? Will I get penalized for canceling my health coverage and how easy is it to cancel