Do I Need a Botox Topup?

I'm 33 and got my first ever Botox injection for glabellar lines 13 days ago. The doctor I went to said he usually uses 25 units so I presume that's what he actually gave! He told me top-ups were free if I wasn't happy with the effect 5 days later. It definitely made it harder to frown but there's a tiny twitch of movement left. Difficult to even see if lighting is poor. I suspect there might be a bit more when I frown unconsciously. Should I go back for more or is this an acceptable result?