That happened a few times a couple years ago in my basement bedroom. Mildew and/or mold started growing right away, and no matter what we did to dry it out, it smelled bad from that day on. When we replaced the carpet, the smell went away and my allergies (which I had thought was something I just had to live with) got much better. While I had the carpet, I remember having clothes that I left on the floor for too long get moldy. That was horrible. I don’t have any suggestion as to how to fix it, but I know from experience that the carpet will never dry out completely (even if it looks dry) and it will make life difficult. Get your landlord on it ASAP, especially if you’re sensitive to allergens like mold.