The sooner you take it, the better.
If you do it within first 24 hours, it's over 90% effective, but if you take it later, this percentage lowers dramatically every 12 hours (for example, if you took it on 3rd day after the intercourse, it would be less than 50% effective).
If you took the pill, it's fine, you wont get pregnant.
You may get your period early than usual or it can be a bit later than usual, but if it's more than 5 days late, take a pregnancy test. I don't think you'll need it though, you took the pill very quickly.