I'm having some issues with my host family?

So I'm a high school student doing a year abroad in Europe, and I'm staying with the same host family for nine months. Now they're really really sweet and generous and they come across as the "perfect" family. But it's been two months and I still feel the same way around them that I did when I first got here: tense, nervous, overly polite, awkward, formal, and uncomfortable. I don't know what to do! I've had a couple of host students before and I've always clicked with them so quickly. Help?! :(

I'm really shy and reserved but you'd think that over the span of two months we'd have been able to "crack" each other a bit more. I'm never able to be myself around them. My host siblings aren't really interested in me and it makes me want to cry because I really really want to get to know them but I just can't click with them. I feel like I'm in a museum and it's all my fault, because they're really open and friendly and I feel like I'm disappointing them by not being more open. I don't belong

Sorry, last update, but what should I do? I'm miserable. I'm lonely in a house full of people. I can't communicate with anyone. And all of this is basically my fault. My host family knows none of this because I always keep a mask of happiness and "everything is ok!" around them, but it's not at all how I'm feeling and I'm pretty sure they know it. What should I do? I really want to get close to them, like a real family, and let my guard down more, but I don't know where to begin.

Thank you <3