12 As for the additional length of the tent curtains, the half curtain that is left over is to hang down at the rear of the tabernacle.

Read Exodus 26:12 Using Other Translations

And the remnant that remaineth of the curtains of the tent, the half curtain that remaineth, shall hang over the backside of the tabernacle.
And the part that remains of the curtains of the tent, the half curtain that remains, shall hang over the back of the tabernacle.
The remaining 3 feet of this tent covering will be left to hang over the back of the Tabernacle.