What the hell should I do..!? T.T '18M' and '18F'

Well, so let there be a girl 'X' and She's the 'one'... So, I met her 2 years ago... And we have been really good.. like! We have been talking till 4 AM and all.. Sometimes We did.. sometimes we didn't! But still! Now, basically I am her Bestfriend and we're really good! She is on the dominant side and I am fine with it... Everything was going fine and We talked that way and all... So, everything was fine! Just this week we had a farewell... And this is the worst trait of me and that is.. being shy! I just don't know why but I just don't Talk to her while being in the friend circle.. well, Our relationship was always being forced by our friends and all... So, this was the day farewell was and She was continuously being said that this might be the last time you might be meeting so, just get a picture... Get a picture.. and many of her friends called me and everything.. but I just kept ignoring or being shy.. and just postponing it.. and In the end everyone had a picture with her... The whole class did.. except me! Her only bestfriend.. and I just don't know.. why!? I did that! She then messaged me and I made it worse by just blame shifting... I just don't know what do I do!? And now I am just regretting that I couldn't even get the last picture and I am just in guilt... So, what do I do!?!! Guys.. help!!