Something can surprise in may different ways, you know? Yes, Paul expected Sgt Pepper to be a success because that's the way he thinks. However, it's been stated by everybody involved that the completed album differed considerably in its final execution compared to Paul's original concept. "So sgt. pepper took you by surprise" meaning the album became different from what Paul expected. Pretty much everything The Beatles touched turned into gold so an album flop wasn't even in the cards.
As to the line "You better see right through that mother's eyes" we're dealing with an English idiom, a saying. For instance, when you look at a child through its mother's eyes, you see it through the bias of motherly love and affection. So John's telling Paul to see right through his idea of what Sgt Pepper was supposed to be to what it actually became and how. John's basically saying that Paul should stop pluming himself on the album being his brainchild and realize that its success and what it became did not rest on Paul alone but on ALL that contributed to it. In other words, don't be so cocksure Paul! It may have been your idea but without us (John, George and Ringo) it would've been nothing!
Sometimes I dream in colors
It always happens when
I find myself with others
Who don't pretend