Should I put a undecided major on my application

So I’m applying to CU boulder through the common app and first it asks: Please select a program, and I chose College of Engineering and Applied Sciences (because that what I want to do obviously). Then it says: Please select a field of study (major) and I don’t know what to put because I’m not sure if I want to do Aerospace engineering, mechanical engineering, or computer science, so should I put down Aerospace engineering because I’m leaning towards that major the most, or should I put engineering open option (undecided). The issue is I’m not sure if different programs are harder to get into, for example are there different requirements to get into aerospace engineering, then in computer science? I know you can change your major, but would it be harder for example to change from a computer science major to a aerospace major. Basically I’m asking is it important to chose your major to get into that major or does it not matter. Thanks so much!