We’re unable to see your return in this forum, but there can be any number of reasons – the most likely being that you claimed too many allowances on your Form W-4, Employee's Withholding Certificate.
Claiming too many allowances results in too little withholding from your paycheck, and eventually getting smaller refunds or owing money once you file your tax return.
Please see the TurboTax Help articles below for more information.
Why did my refund go down compared to last year's?
How do I update my 2020 withholdings and print a new W-4?
What to know about the new 2020 IRS Form W-4 Employee’s Withholding Certificate