The error is in italics and bolded for you:
THERE'S NOW SEVEN NEW FLAVORS!
The correct way to write the sentence should be like this:
THERE ARE NOW SEVEN NEW FLAVORS!
The reason it is There are and not there's(there is), is because you are talking about the new flavors being in the present tense form. Like... it's hard to explain, I guess...
Hope this helps!!!!