He said i love u, what do i say?

my boyfriend and i have been together for abt 4 weeks and he makes me very happy and i have extreme felling for him. well today he told me that he loves me. i was shocked i was hoping maybe later down the road we would fell that way. But i feel likes its too soon. I don't want to say no because i care for him . what do i say to him Im so stuck help please