Speaking as an American: The term "GPA" is normally understood to mean a number. You could round off, but "I had a GPA of B" sounds incongruous to me, like saying "My favorite color is 7".
That said, the normal way to say this in the US is, "I graduated from Fwacbar University with a GPA of 3.2". Or if you got an ...
In my opinion, the best and most concise book on writing good English is Strunk and White, "The Elements of Style."
Use the active voice.
Use simple constructions.
"The unexpected 10% cost overrun was due to unexpectedly high labor costs."