Cal Poly is a very solid engineering school. The university's academic is rigorous and challenging.
The issue is that there are Cal Poly Engineering students with 3.8+ GPA applying to Med schools as well. Not to mention there are 3.8+ GPA MIT/Princeton/Stanford and other tier 1 engineering graduates applying to Med schools.
The medical schools you mentioned, Stanford and Harvard, have med school acceptance rate hovering around 2-3%. To stand a chance of getting in to either you need to be an ABSOLUTE academic star at your undergraduate, along with great school/social services record, outstanding recommendations, top top MCAT score, great in-person admission interview, and a great hook on why you want to be in medicine.
A 3.3+ GPA at Cal Poly is respectable, but unfortunately (not to be harsh or discourage you), you were not the rock star within CP. Thus, it might be a long shot at the aforementioned institutions for medicine.