The Qu'ran is very specific about how the hijab/khimar (as in the headscarf) should be worn. It says we should pull the headress down so that it covers our jube (chests---the va va voom ladies). If you are not covering your chest with your hijab you are not wearing Islamic hijab. I hate to break it to you but you are wearing Christian hijab. Jewish women were supposed to cover their hair, and the Christian women to cover the hair (their wrap style was often so that the neck and hair were covered but not the chests). I'll do a post on the differences inshaAllah.
I love the bright styles and European aura Turkish hijab styles give, but the one thing I can't stand about them is often the lack of chest coverage in the fashion shots. I can always wrap my turkish hijab to give lots of chest coverage, but I wanted to share this Turkish hijab fashion pic that shows some more than awesome chest coverage. Do you like? Would you wear this style?
And to answer Inspired Muslimah's question in the comment section, I don't think an Al-Amira counts as hijab if it isn't long enough to cover the chest also. I always wear an al-amira under my shaylas to get the coverage I am supposed to have.