What do you think of me telling my teacher I did the whole project by myself?
Why would you tell the teacher you did the whole project? Did you?
Yes, I did the whole thing by myself. I'm really proud of my achievement.
It's great that you were able to finish all that work by yourself, by all means be proud of it. You put in your best work and managed to get it all done by yourself. Keep striving to do even better.
Whatever, I'm going to brag about it to my teacher.
It's one thing to be proud and want to tell someone but you shouldn't do it just to be bragging. Bragging is a good way to have people annoyed at you. Be proud of your achievements but also try to be humble.