this is just my opinion but i would be wary about just saying you are uncertain. this is the path i took last app cycle and it got me rejected. i got an interview and when i asked them why i wasnt accepted they told me that my adcom wasnt sure that i was serious about being a dr. after reflecting on it, i have concluded that i would not write that again or say that in an interview. in fact, i have changed my app to say the opposite. i have made a strong case for what i want to do and why
now i dont think you necessarily have to say that you are for sure going to do xyz, but instead you should really think about it. what aspects of your clinical experiences did you like? you MUST have liked something. For example, you like the idea of working under pressure so maybe you want to to Emergency Medicine.
I think its important to reflect on your experiences and your personality make some conclusions about which fields will best suit your needs (i feel like i just wrote another secondary... hahaha). pick one or two and discuss why they might fit with your personality.
DONT just say that you dont know. i believe it shows that you did not take enough time to truly reflect on why you are really going into medicine.
but that's just my opinion