How long until waiting to take more advil? I think I took it too early?

Ok, this is going to sound dumb. But I'm 16 years old. And I still take the liquid, children's advil because i cant swallow pills. Anyway, I took some early this morning, waited a long time, then took some more, but then i just took some now and i think i took it too early. Does it really matter since its childrens advil and im a lot older. I took around 25 mls. my mom says wait around 4 hours, but i think i only waited 3..