I only changed one question (can I be claimed as a dependent) on my refund and its affecting my numbers dramatically. Why?

[PEK]

If you indicated you can be claimed as a dependent by someone else, you would not be entitled to the exemption deduction and/or perhaps the standard deduction.

[DavidS127]

Your standard deduction is limited when someone else can claim you as a dependent. If you can be claimed as a dependent by another taxpayer, your standard deduction for 2019 is limited to the greater of: (1) $1,100, or (2) your earned income plus $350 (but the total can't be more than the basic standard deduction for your filing status).

So, if your earned income is substantially less than the $12,200 "regular" standard deduction (i.e., when you aren't claimed as a dependent on another return) it can make a big difference in your taxable income.

Also, you don't qualify for the Earned Income Credit (EIC) if you are a dependent of another person.  That can also make a substantial difference in the refund for which you qualify.

Starting in 2018, the exemption amount is "zero" so not counting you exemption no longer makes a difference in taxable income.