You may want to check your visa. Brazilian tourist visas are for 90 days, not the more vague '3 months', to avoid such confusion.
Example from Wikipedia:
Of course you may have realised this already, as in your case, 90 days including Feb 25 IS May 25, but for future readers I'm clarifying this.
Your visa is valid for this entire period, and as you realise, is valid for multiple entries within this time.
Obviously, entering on the very last day MIGHT raise some questions at the border - but as long as you can show them something like your hotel accommodation that night OUTSIDE Brazil, or your bus ticket or flight or something - basically evidence that you're not planning on overstaying, then legally you will be entitled to enter.