Using the marks you made earlier, sort the wires into two bundles: postive and negative.
Trim, strip, and solder each bundle together.
Slide a piece of heat shrink tubing over each battery wire. Solder the black battery wire to the negative bundle, and the red battery wire to the positive bundle.
Before you shrink the heat shrink tubing, carefully test your circuit by loading up the battery pack and switching it on.
If all your LEDs light up, you're good to go! If none light up, you likely have a power problem. If some light up, you likely have some that are wired backwards. Make any necessary fixes and carefully shrink the heat shrink tubing with a heat gun, hair dryer, or lighter.
Use floral tape to wrap the wires to the stems.
Arrange bouquet in a vase, your bridesmaid's hands, or your prom date's wrist. If you're using the small wearable battery holder, don't forget to pack a few spare CR2032s!