How to make my application stand out?

I'm hoping to go to the University of Denver for college next year. I've worked hard throughout high school to get straight A's and B's (3.8-3.9 gpa currently). I switched from regular math to honors math junior year and am currently doing well (I'm a senior now). The problem is that my involvement and leadership roles aren't great. I've done multiple things, but haven't had commitment to them (other than academics). I've done a lot of volunteer work in the past 4 years, but I've only been in a few clubs and have been on and off with those. I would have joined more clubs throughout high school, but I wasn't very good at making friends, so I had trouble getting connected to a club, and I dropped them. It wasn't until this year that I've been more confident and social. Over the the summer I volunteered for kids with speech problems and finally landed a babysitting job (everyday after school). I love the job and I do very well. Since I started, the parents told me that the kids have been much more manageable and in better moods.

Once I'm committed to something I can do very well at it, I just had trouble finding something to be committed to until now. But how do I note this in a college application without making it look like I'm making excuses? Or rather, how do I put this info together to look impressive?

Also, my ACT and SAT scores aren't IMPRESSIVE. They're okay, but not great: 24 on the ACT and 1090 on SAT (math+critical reading).