You need 3 months of statements because a 2 month statement today (28th) would be all of July and August to date so not two complete months. The danger of changing banks is it might show as a withdrawal one day and a deposit the following day so the closing balance drops to zero for one day. Take care.
If, when you re-entered the country, you were already on an Extension of Stay (not on a Non-O Visa which is 90 days) then your next 90 day report is counted from your date of re-entry. If you were on a Non-O 90 day stamp when you r-entered then your first 90 day report will be 90 days from your extension date.