smc

Substituting $x=-3$, we get $$f(-3)=81a-9b-3+5=81a-9b+2.$$ But $f(-3)=2$, so $81a-9b+2=2$, which means $81a-9b=0$. Then $$f(3)=81a-9b+3+5=0+3+5=\boxed{8}.$$