Moldy Futon? I’m an abroad student

Hi! I just moved to Japan as an abroad student. I'm in the homestay program with my school, so I was placed with a host family. So far they've been really sweet! I just arrived, barely over a week now, and I have a futon.

My family explained the basics of a futon, which is to either put my futon up to dry once a week or use their portable dryer thing to dry it. They don't know a lot of English and I don't know a lot of Japanese, so it was a bit confusing when they were explaining how it worked. I've never slept on a futon before and I was mainly judging when to put mine up/out by when they suggested it and when they did it themselves (which was once a week).

I had today off from school and I'm going to the city this weekend so I figured I'd get a jumpstart on my laundry, as well as air out my mattress. Well, I was airing out my futon and it's super stained! I don't think it looked like this last week when we aired it out but I have really bad memory. It was super wet too, and even the floor was wet where my futon was on the floor. I also noticed a bunch of black dots all over it that I don't remember seeing last time either, but my host family did most of the heavy lifting and showed me where everything goes so it's possible I missed it. Is this mold? What should I do? I'm the only person in the house right now, everyone is working and I really don't wanna have to deal with the embarrassment of already making my bed moldy… I'll post a picture in the comments of the suspected mold.

What should I do?

Edit: I don't have a tatami mat beneath my futon. It's just wood flooring. I live in central Japan. Also it's on the second floor and I don't use the heater in my room very much, so it's generally pretty cold and I'm a very warm bodied person.

My host mom came home pretty soon after I posted so I told her and showed her, she said it's mold but not too much. She said to start putting my bed up every day so I'll be doing that. We're washing some of the blanket covers and she suggested I use a thinner blanket from now on, so I'll see if that helps. We put the futon outside to dry but I was planning on taking a trip this weekend so maybe I'll leave earlier than I planned to let the futon dry longer. Thanks for all the advice!

by -g-r-i-f-f-