Guilty about good graduation grade?

I got my marks earlier today, hoping for a 2:1 but expecting to get a fairly average 2:2, maybe low 2:1. Instead it turns out I got a first class degree, with the second highest mark in the class, but I feel terrible about it. My grade was published along with my results, so I checked them to be sure and they add up fine. I didn't cheat and put lots of effort into my work all the time, and know I'm fairly self-critical, but even though I'd been told I could get that mark I still pegged myself lower. My friends and family keep asking what I got, and every time I'm asked I feel worse. I haven't been able to tell anybody yet because I feel so guilty about it, but I don't know why. One of my housemates is quite big headed and has always regarded me as some sort of idiot, so when he asked what I got, I explained that I didn't want to talk about it and now I'm fairly sure he thinks I didn't graduate or got a low third or something. I want to feel proud of my results and tell people, but instead I feel really guilty. My course has shut down now, so I was in the last year that would ever be examined, so I'm also scared people will think the university boosted my grade, even though it was all externally moderated because there were so few people left in the class at the end. I know I've worked just as hard as anybody else, and should be proud of my marks, but I still can't help feeling bad about it all. I feel like if I say I've got a first it'll sound like boasting, and that's the last thing I want as I'm rather shy and would rather just hide somewhere. Should I say I got a second, or try and be proud of my real grade?