Not bad. But the first sentence can be deleted. You're telling them something they already know.
People have always told me I am full of potential, but I don't feel challenged by the current academic pathway I am taking, to make the most of my potential.
This here is not a good start. You could tell what makes you have potential, somethings you previously done. What type of person you want to become when you finish the IB program.
If I were accepted into IB, I would contribute to the academic and extracurricular components of the IB Programme with my creativity and unique way of reasoning and analyzing.
This here is what I believe could be a strong thesis. Build on what you have here.
The IB Programme is a great experience that will help me become a more responsible, well-rounded of a person, and prepare me for life after high school.
The last sentence is another where you could explain more. Talk about your ambitions after high school, if you have decided on a career path. The rest of the essay are simple fillers, but you can work on them and make them unique. Hope this helps. :)