I feel like I'm letting them down, so to, so to speak.
( I ( ( ( ( feel ( like ( I ( 'm ( ( ( ( ( letting them ) down ) , ) so ) to ) ) ) ) ) , ) ( so ( to speak ) ) ) . ) )
(ROOT (S (NP (PRP I)) (VP (VBP feel) (SBAR (IN like) (S (NP (PRP I)) (VP (VBP 'm) (VP (VP (VBG letting) (NP (PRP them)) (PRT (RP down))) (, ,) (ADVP (RB so)) (VP (TO to)))))) (, ,) (S (RB so) (VP (TO to) (VP (VB speak))))) (. .)))
I am certain that I am not meeting their expectations. 
( I ( ( am ( certain ( that ( I ( ( am not ) ( meeting ( their expectations ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP I)) (VP (VBP am) (ADJP (JJ certain) (SBAR (IN that) (S (NP (PRP I)) (VP (VBP am) (RB not) (VP (VBG meeting) (NP (PRP$ their) (NNS expectations)))))))) (. .)))