If the pins are too long that they cannot be safely pinned inside the bouquet handle, you can cut the pins down to a shorter length.
Always use safety precautions, as the sharp ends of the pins can go flying off into space. Use safety glasses to protect your eyes.
To prevent that, always bury the shank of the pins deep into a stiff block of styrofoam. I then use a heavy pair of wire cutters to snip the steel shank to the right length.
The pin has to be long enough to hold the ribbon firmly, yet short enough to bury the end into bouquet stems.
To be sure the pins stay in place, I use Oasis floral adhesive to lock the pins into place.
I actually insert the shortened pin into the adhesive tube, coating the shank with glue. Then pin down the ribbon in an even pattern. The adhesive will lock the pins in place after the adhesive dries.