I will tell you this. Like I said before, I know 2 graduates from the design institute. One works for me now, one worked for me during mothers day a few years back, and we are friends to this day. both are very good designers, and both are very young, 24 and 28.
so i really have faith in that school, i've never been there, never even heard of it until the one girl worked for me during mothers day.
you'll need to find a shop that will be willing to coach you while you get comfortable in your own designer skin. and don't get discouraged if they say they don't like something you did.
when my mom was first training me, i'd make something, if she didn't like it, she'd tear it apart, LITERALY, and make me re-do it.
a lot of shops don't want to take on someone who doesn't have a lot of "shop" experience. there's more to filling orders than just making pretty designs. you'll have to become part psychic, know how to sell flowers, price an arrangement (that includes ALL flowers, foliages, tape, wire, container, TIME etc) blah blah blah.
that's why you're having a hard time finding a job. just tell your interviewer you'll do what ever you have to do to get the job....
my best advise is pay attention to everything. listen to them on the phone with a customer, observe them with a walk in client, pay attention to the things that sometimes gets overlooked such as debris on the sales floor, empty buckets in the cooler, buckets left with one flower in it (use that flower!!) finger prints on glass doors, finger prints on sales counters or water on sales counters, plants being dry, etc. all of that, and more, makes a flower shop go round.
with all that said, try not to irritate the current staff with your efficiency, yes, it does happen, no one wants to be shown up. really all they would be shown is their short comings.
it's a tough business, but once you get it down, any shop would love to have you.