Looking at Fed total assets [0], the Fed's sold off only a fraction of what it took on during the crisis and QE.
[0] Fed total assets from FRED: https://fred.stlouisfed.org/series/WALCL
[0] Fed total assets from FRED: https://fred.stlouisfed.org/series/WALCL
The fed also expanded the balance sheet by selling long term bonds, which offered relatively lower rates in comparison to short term notes and bills, this provided the cash infusion needed for QE to stimulate the economy.