I will qualify for the full stimulus with my 2019 taxes so would like those to be used if bill passes this month.
If your tax return has been accepted by the IRS, then there is no possibility to withdraw or stop the process.
The IRS may use your income from your 2020 tax return to determine your eligibility for the coming stimulus.
No you cannot halt it now. And we don't know yet how any new stimulus will be handled or if it will even be retroactive to 2020, or involve the IRS.