but it sounds like you got caught up in assemblyline diver manufacturing. Even if you really really sucked (and I'm not saying that's the case), your class instructor should have recognized your needs and dealt with them. No two people adjust to the requirements of diving with the same degree of ease and any good instructor should and will make allowances and not send you away from a lesson without either helping you out or suggesting you need extra tutelage or perhaps explain diplomatically to you that you're just a klutz and shouldn't risk your life in the ocean. 8)
I can remember our instructor giving some extra time to some students in the pool while his assistants took some of us off to play with a few more esoteric skills or just have fun in the water.
We were also lucky in that we got to do our open water dives with the same instructor and assistants who taught us in the pool. Divers tend to quickly forget how nervous we were when we headed out for those OW dives. Having familiar faces to guide us along is a bonus as it eliminates some of the discomfort, and Heaven knows there's enough of that on your first venture to open water.
Having lousy equipment only compounds the problem, and should get you some kind of compensation in the form of extra instruction time. One piece of rental may fail, but to have the mess that you describe suggests crap gear. Perhaps it's an indication of the quality of the instruction as well.
I'd be going back to my instructor and saying that the checkout guy says you weren't adequately prepared, and politely suggest that you want your money's worth, and you want better equipment for the OW checkouts.
If they can't deal with that in a businesslike way, then write off your money spent as a bad investment, say so to the instructor and/or shop, and go find a competent and obliging source for training. Diving ain't rocket science, but it sometimes takes some patience to master to the point where one is at least a reasonably competent beginner diver. You paid the money and should be entitled to the service, or at least an honest assessment. And don't forget the name of the shop and the instructor when you become a diver, because others will be asking for recommendations. You want to make sure no one gets treated like you did.
JF