Hi! If you let me know which ending(s) in particular you're trying to get, I can point you towards which choices should be able to get you there!
In general, an 'impactful' choice is one that shows Jessie crossing what would typically be considered a boundary (standing out from the crowd through bad behavior), and a 'romance' choice is one that expresses Jessie's feelings. For example, the first-letter sign-off "Sincerely, your secret admirer. PS I know you're a girl." gives +1 romance for the secret admirer line (as opposed to saying 'a friend' which gives neither romance nor impact) and +1 impact for the postscript since outing somebody to their face isn't the most socially acceptable thing to do.