Haas looks much more at extracurriculars than they do grades. Given that you did fairly well in the classes required to apply, and your overall GPA is higher than 3.5, you shouldn't worry too much about your grades. Once your GPA drops below 3.0, you have nearly no chance unless you're really awesome at ********ting why you're awesome and are a veritable Mark Zuckerberg 2.0.
Haas acceptances have always been a bit of a coinflip in some ways, but usually, the trend is that if you do a fair amount of extracurriculars, show passion, and don't suck at school or the extracurriculars, you'll have a good chance at getting in.
Summer is fine and everything, but try not to get too greedy. Summer classes are incredibly intensive, so it's advisable you don't take more than one at a time if you're really looking for a job. For extracurriculars, it's too late to really apply to be in cabinet for anything, so you might have to make it up for the next semester by applying to a lot of things or finding meaningful jobs (the former is not quite advisable).