What architecture programs are looking for in a portfolio are potential and teachability, not accomplishment. Your portfolio should demonstrate creativity, a grasp of one or two artistic media, especially drawing, and a sensitivity to design in its overall presentation. Colleges know that a high school student may have had limited opportunity and resources and don't expect professional level work.
A semester's worth of art/drawing isn't much time to put together appropriate material, but it's doable. Perhaps you could find an artist or art teacher willing to work with you over the rest of the summer or take a Saturday class at a museum or community center.
Most importantly, before you commit to a B.Arch you need to be 110% sure that architecture is for you. The B.Arch is a rigorous and intense program that doesn't leave a lot of room for academic and career exploration.
You indicate that this is a change of direction for you. You might want to take a gap year to catch up and reinforce your decision. Or focus on universities that allow you to delay the commitment to architecture until you've had a general exposure.
The problem with some B.Arch programs (Cornell included) is that if you have a change of heart and want to switch to liberal arts you may not be able to graduate in four years. which of course means additional expense.
The BA/BS + M.Arch route to architecture is a good option, but be aware that it costs more and takes longer than the B.Arch.