I also took an intro to arch course and come from a non-arch background. I'm beginning my M.Arch I program this fall. My advice would be to really emphasize process and showcase your thinking and intention behind your portfolio works and design decisions, particularly the ones that will come from your summer program. Aesthetics and form is all nice to look at, but if that's all one shows it will fall short, as schools (rightly) expect some underlying logic and intention behind the work, be it utilitarian, social, cultural, etc. I also recommend treating the portfolio itself as an exercise in design, pay attention to white space, limiting use of text, etc. Good luck! Anything's possible if you work hard.

The INARCH program will help you decide whether the studio environment is something you want to immerse yourself in for 3 years as an M.Arch student. It'll also teach you a few different graphic programs (rhino, illustrator, indesign, and photoshop). It doesn't teach you that much about design, but it gives you a good idea of Berkeley's pedagogy.

If I were you, I'd learn how to use rhino and illustrator to at least an intermediate level. It's a real shame when you have ideas, but cannot execute them due to lack of software knowledge. But when it comes to the studio, you need to be able to use your hands, get physical with materials and blocking for programming/design, and really know how to sketch for communicative purposes. 

If you're in love with art, understand that architecture is not art. Architecture is 10% art, 90% engineering/structure/everything practical. If you have the ability, look for internships or apprenticeships in the next year. Network and talk to as many architects as you can so you understand what the field is like rather than what school is like, because they are very different. Know that this is a very, very long career path.

Have fun! I'll be one of your GSI's this summer (=