As a rising senior, what should I be doing over the summer to better my chances of getting into a good school?

I recommend attending one of the architecture programs listed in this CollegeVine blog post. Beyond summer programs and the college architecture course you found, it would also be a good idea to take AP Art History and AP Calculus. This other blog post has more advice about class and other ways to improve your application. Hope this helps!

One if not the most important thing architects look for in young designers is their ability to communicate design ideas through their sketches, drawings, renderings or CAD files. The designs themselves do not have to be engineered or believable from a fabrication perspective but they need to look fresh, innovative and unique to your own style and aesthetic. I'm not talking about houses or buildings necessarily but any sort of design whether it's car design, fashion, shoes, product design, landscape design or drawing a yacht.

When you look at design itself, one can see a similarity of intent whether you are designing a watch or a pair of running shoes. Therefore in my opinion, your design portfolio is the single most important thing that will determine whether you get admitted to a top architecture school or not.

I would work on your design portfolio each and every day during the summer before you apply to architecture school. If you are not already an expert artist, I would enroll in some art classes. Your ability to create visual impact and intent will serve you best in the future.

Good luck.