The $3 trillion includes $1.37 trillion already borrowed in April. That implies additional borrowing of $1.63 trillion in May and June. May typically has light net new borrowing. May 2019 net borrowing totaled $67 billion.
The $3 trillion estimate is an increase of $3.06 trillion above the Treasury Department’s Q2 estimate that it posted in February.
See Liquidity Trader for ongoing in depth analysis and outlook.