Weight will it affect the results?

The upper weight limit for Plan B is 150 pounds (10 stones 10 pounds/68kg).
Anyone over that limit could use the other emergency pill (Ella (Ulipristal Acetate)), or, if that is unavailable, may want to consider having a Paragard IUD fitted by a doctor, as well as Plan B. A Paragard IUD may prevent a pregnancy implanting, if the Plan B does not manage to prevent the pregnancy.
There are women who are over the recommended upper weight limit for Plan B, & say they did not become pregnant when using it, but, as with every use of emergency contraception, they'd have to know that they otherwise would definitely have become pregnant, had they not used Plan B. That's obviously impossible to know.
In other words, it may just be that they would not have become pregnant on that occasion, even if they hadn't used emergency contraception. It's impossible to know the emergency contraception was what prevented pregnancy.