flea treatment do i need to get new one?

we have had quin for four weeks now so i have just put on her second flea treatment given to me by the vet 4 wks ago (she put on the first one when we registered quin with them) it is advantix spot on solution, i have just noticed though that it says for dogs 10kg to less than 25kg, which she was when we first took her (23.4kg) but last week when we took her for a weight check she was 26.6kg.
my question is as i have put treatment on already before realising this do i need to take her to the vet to get another one? can she have another one if i have already put it on this morning? will this one be ok til i go to the vet again? (we take her every 4 wks as she is so underweight at the mo so will see the vet before she is due again)
i have active arthritis at the moment and my husband is away this week so getting to the vet is a very painful experience for me however if advice is that she needs to go then we will take a very slow stroll down asap
thanks guys dont know what i would have done without this site x x

hi,
you will of underdosed her (sorry ) i would call the vets and see if you can pick up one application of the lower strength to make up the difference,they may even post it to you but DO NOT put another one of the strength you have,advantix is a pretty hefty insecticide.(why not try advocate if you dont have a big tick problem)
hope this helps