The refund amount that you see in TurboTax doesn't really mean anything until you have entered all your W-2s, because your actual refund is based on your total income and the total amount of tax that was withheld.
Each W-2 has an amount of income and also an amount of tax withheld. Depending on the amount of tax withheld in relation to the amount of income, each W-2 that you enter could make your refund higher or lower. And how your refund changes as you enter each W-2 could vary depending on what order you enter them in.
Also, your standard deduction reduces your taxable income. But you only get one standard deduction. The first W-2 that you enter probably uses up the entire standard deduction. So the income on the additional W-2s is fully taxable. Adding more taxable income, with no more deductions, reduces your refund.
