It depends on your accuracy of your tests. You changed 10%, then 20% again. That means that 28% -> 14 gallons of you water is new. Therefore if you should see roughly a 1/4 of a reduction in your ppm... I know that I can't tell that much difference in my tests. They aren't that accurate and its hard to read changes unless they are large (orders of magnitude different). Am I right?
In my opinion (which isnt worth much in this community of experts) all you can do is let it sit and hope for the best, or return the puffer to the LFS for a few weeks until your tank finishes cycling.
If the bioload is already stressed, the puffer might introduce enough of a bioload to cause some serious problems. When introducing any fish to any aquarium (well almost any), the resulting increase in bioload will cause a spike in ammonia, nitrites, nitrates (I mini-cycle)... Keep an eye on the levels, if they keep increasing you are going to have to do something. Hopefully, they will be calming down and the tank will finish cycling.
If you have questions about the value of my opinions, please refer to my title:
Ignorant and Oblivious...