i would say don’t risk buying them and having them not fit if you can’t return them. a lot of students buy mattress pads/protectors before putting on the actual fitted bedsheet and if you are planning on doing that, then it adds extra bulk and twin sheets definitely won’t fit. even if they do fit, you’ll have to stretch them constantly and probably end up ripping them. i’m gonna assume you’re a freshman, so just invest in some ok-quality twin xl sheets/bedding that you can use for the next couple of years. target, bed bath and beyond, etc. will have student discounts and college sale periods, so you can save a little bit of money. More on reddit.com

Try calling the store during their business hours tomorrow. I'd just look around on Amazon, Target, BB&B, or even Walmart. I also wouldn't spend a whole lot of money on your dorm bed sheets that you'll only use for a year maybe two then probably throw them away since twin beds are so damn small. You could sell them but I just threw mine away they'd seen enough. When you get an apartment is a slightly different story because you can actually make it yours, and your not splitting a room in half with someone else. I wouldn't order them from the catalog your school might have advertised them in. They're not cheap and are really poor quality. Buying from one of the stores I mentioned would have been cheaper and lasted longer. Same goes for all the bathroom/dorm shower kind of accessories. I would have been better off getting stuff from BB&B instead of that magazine. I might just be an ignorant male but I feel like BB&B has enough patterns that are cute enough for a dorm. And hell if you end up lofting your bed hardly anyone will even be able to see it. More on reddit.com

You haven't even told us what country your "standard" is. You need to look up the actual size of the objects in question. You can have a duvet (with correct sized cover) of any size on top of a bed, that doesn't need to match exactly. Maybe the person you saw had an ikea duvet and duvet cover. More on reddit.com

At fully extended it is the same size as a twin mattress. They do sell sheets for the smaller sizes, but you could also just take a twin sheet and fold the excess under the mattress and it could work. More on reddit.com