@JoannaD don’t be too hard on yourself As with all new ideas and new efforts, unforeseen problems happen! The same comb collapse happened to me too, and it killed my queen which I didn’t know until I found an open queen cell later on!
Dawn and Peter gave you all the important points you need to go forth from here, but I’m replying to add a bit of context that I hope will help. When Flow went about putting together their amazing kit, they weren’t only focused on the harvesting of honey - they wanted to provide a whole package with equipment and information to support beginner beekeepers in the best way possible, for an international audience. A lot of newer ideas about how to control varroa mites were being discussed, after data from a couple decades of widespread miticide use showed bad effects on bees. Many well-known beeks promoted using foundationless frames, so bees would build cells to their natural size, as an important component of non-toxic mite-management. So, the Flow brood boxes all came with foundationless frames, and they released a nice set of instructional videos to point out details like how to lift and manipulate these frames, and also how to fit them with foundation instead.
When you’re a beginner, some of that info gets lost and it’s hard to appreciate the inevitabilities of physics until you witness them in action
You can keep letting the bees build natural-sized cells, but it’s clear that the large vertical space of deep frames needs to be supported in some way - so if you opt for foundation, you can choose ‘small cell’ kind. Or, you can modify your frames with more structure like I did, by affixing 3 bamboo skewers inside the frame, spaced across vertically.
Good luck & let us know how things go!