Scorpion?
So you say that while creating the seal that also made Sakura's natural chakra reserves increase? That would make sense.
Then only after the seal is complete could she actually access her newly increased reserves of chakra.
For example, Sakura's natural chakra reserves are of 50. But she locked away part of that 50 in order to create the seal. And because of constantly saving chakra that made her reserves increase up to 500, but she could only access all of that after the seal was complete.
HAHAHAHAHAHAHA!
Like ramen says, Sasori is Scorpion, I've always seen him as the Scorpion of the Red sands ^^"
and yes! I think, without the seal being fully created, even if she had the chance to stop creating the seal to use the rest of her chakra, she wouldn't have any of that chakra to use! That's why it did not benefit her to stop the process of making the seal during her previous fights.