On the patch, question!!

So I put my patch on , but then things got crazy and I thought I changed it but I didn't. And accidently dtd during a week I would of been fertile. I know if u use the patch correctly you don't have a "fertile" week but I was just reading and it said it only has enough in it for 2 days past patch change date. If not then it becomes null and void... chances of pregnancy? We had a mc in july and had planned to wait till next yr to ttc. But if it happens it happens if it doesn't it doesnt...