Fold on score lines in opposite Z-folds, as shown . . .
. . . and glue the narrow one to the front of the card base, as shown.
Using the remaining 2 1/8" x 11" strip, score at 7/8", 3 5/8", 4 1/8", 6 7/8", 7 3/8", and 10 1/8". Fold as shown.
Apply double-sided adhesive tape to the folds, as shown . . .
. . . and repeat on the other sections on the opposite side.
Remove paper backing from the double-sided adhesive tape and carefully fit the folded strip into the box in the card base.
Here is a close-up of the inside of the pop-up box portion of the card.