Do I absolutely have to check yes if someone can claim me as a dependent but isn't going to claim me? I am a college student but I pay for more than half of my expenses?

If someone can claim you then you absolutely have to check the box reporting that, even if you are not claimed. I can’t determine from your post whether someone is eligible to claim you. 

You are not eligible for the stimulus payment if somebody CAN claim you as a dependent, whether they actually do or not. 

"I pay for more than half of my expenses". 

 

That might mean that you do not qualify as someone's dependent.  It depends on HOW you pay for half your expenses.  Scholarships are considered third party support and not considered as paid by you.  529 plans, where you are the beneficiary, but not the owner,  are also not support provided by you.  Student loans, in your name are support provided by you, unless the parent co-signed. 

 

A child of a taxpayer can still be a “Qualifying Child” (QC) dependent, regardless of his/her income, if:

1. He is under age 19, or under 24 if a full time student for at least 5 months of the year, or is totally & permanently disabled
2. He did not provide more than 1/2 his own support. Scholarships are considered third party support and not as support provided by the student.
3. He lived with the parent (including temporary absences such as away at school) for more than half the year

 

So, it doesn't matter how much he earned. What matters is how much he spent on support. Money he put into savings does not count as support he spent on him self.

The support value of the home, provided by the parent, is the fair market rental value of the home plus utilities & other expenses divided by the number of occupants.

The IRS has a worksheet that can be used to help with the support calculation. See: http://apps.irs.gov/app/vita/content/globalmedia/teacher/worksheet_for_determining_support_4012.pdf