If you're going for medicine your ps should be specifically medicine, the course is so competitive (as you know) you need to show that you are absolutely dedicated to becoming a doctor. I would even go as far as to say if your heart is not absolutely set on doing medicine, I wouldn't bother at all. But that is my opinion.
Chem Eng is a very different path to medicine and not necessarily an ideal choice for a starting degree if you plan on doing medicine as a second degree. If you do choose Chem Eng, just make sure you like maths! There is a LOT of maths in Engineering degrees, I don't think people always appreciate just how much.