H1-B and Green Card

I got my bachelor in US 2 years ago and I did 1 year of OPT afterwards. Then, I am doing my masters now and will graduate next year. However, i found out recently that I was not supposed to take a job which is not related to my major. And, that is where the problem is.... during my OPT, i was working as a cashier for the first 3 months. I really did not know this rule until recently I heard from my friend. So, would it affect my future if I am going to apply for OPT, H1-B visa, and green card? If so, is there any ways to compensate for that? Honestly, I really don't know this rule beforehand and I am not violating this rule on purpose.

Thanks.