Hi! Both of your SAT & ACT scores are totally fine for Penn and retesting will likely only hurt you. A 34 is almost exactly equivalent to 1540, according to all conversion charts I’ve seen, so there would be no reason to withhold your ACT and submit your SAT. Talking about your interest in PPE is good, but it’d probably be best to emphasize how your current passions make you a good fit for this – emphasizing Model UN, perhaps, and/or joining organizations that show similar interests. Penn & its peer schools value extracurricular depth, especially pertaining to your major, so that’s what I would focus on! Literature is a very tough test, but I think US/Math/Bio are good options, particularly if you’re enrolled in corresponding classes this year!
Best of luck! 
Chance me back? http://talk.collegeconfidential.com/what-my-chances/1966406-chance-me-upenn-ed-yale-brown-princeton-etc-will-chance-back-p1.html