Sounds like you're not really sure of yourself, your self esteem? Other people being glad of their accomplishments has nothing to do with us and ours and you may or may not mess up in the future but if you are sure of yourself, you won't worry about that either way! Take a bit of pride in your own accomplishments and look back at how you seem to do well and relax in that "habit" of yours!

I use to procrastinate and get anxious about my work and the future but then I'd look back and realize I always get the work done well, one way or another, so there was no reason to get on my own case! It's nice to "allow" myself to just do my own thing and not spend so much time directing with my head. When I get "uncomfortable" I'll start the work and get interested and do well! You have had 10 years to establish your habits that appear to be effective for you; be proud of your good work habits and know they are part of your "character" and can be relied on; you can rely on yourself! Congratulations on your great grades so far.

I would learn to rib your friends a little about what you see as "bragging", congratulate them and tell them to "keep up the good work" and maybe remind them, "Watch out, you know what they say; pride comes before a downfall!"