no.

on the first week you need to make 4 posts for every day of participation
because weekly confirmation are done once a week (every thursday) so someone who joined the campaign in the middle of the week doesn't have to make the whole 25 posts for that week

so let's say someone joins on monday he will have to make (3 days) * (4 posts a day) = 12 posts...
and this guy will get 3/7 of that week reward


in your case,because you joined  at the beginning of the week
you need to make 25 posts
and you will be rewarded with the full reward for this week