I stand amid the roarOf a surf-tormented shore,And I hold within my handGrains of the golden sand— (12-15)
The speaker definitely emphasizes what he's doing. Note the way "I stand" and "I hold" are at the very beginning of their respective lines. It's almost like he's trying to convince himself that these actions—standing at the beach, holding sand—are actually happening, and not just part of a dream within a dream.
Is all that we see or seemBut a dream within a dream? (23-24)
The speaker's final words are a question, not a declaration. He's being totally skeptical here, refusing to give an answer to the question of whether or not really is just a dream within a dream.