Hmm, well since it sounds like you received the news relatively recently, it could be the case that they haven't sent out any feedback yet. You could try contacting Siemens to ask if you'll receive judges' comments.
I have seen the advanced project portion of the website but I haven't been able to find anything that would pertain to me, as I am done with my project. I'm thinking that maybe style was the issue? Or maybe it was too lengthy and not organized enough?
Since you seem concerned about your paper, it could be helpful to look over the tips on writing, and it's not too late to tweak your data analysis and conclusions.http://www.sciencebuddies.org/science-f ... port.shtmlhttp://www.sciencebuddies.org/science-f ... ysis.shtmlhttp://www.sciencebuddies.org/science-f ... tips.shtmlhttp://www.sciencebuddies.org/science-f ... tips.shtml
(for competitions where you make a presentation in person)http://www.sciencebuddies.org/science-f ... cess.shtml
It's hard to say what problems there might have been with your style, length or organization without seeing your report. Occasionally students post reports here requesting feedback and usually some expert will find time to take a look. Based on the project question in your profile, you'd probably have the best visibility by posting in 9-12 Life Sciences -- but definitely specify that you're entering advanced competitions.
Some other sites I've looked at also told me that always write in the active voice though it is not conventional for traditional science papers. What do you think?
It's becoming more common to see the active voice in peer-reviewed publications in some circumstances. "We present new data regarding..." sounds normal to me, but "I prepared samples according to the following procedure..." does not; I'd expect to read "Sample were prepared...". Generally, writing mostly in the passive voice is a safe option; the active voice might sometimes simplify sentence structure and make things sound more natural, but you risk sounding amateur-ish. Having lots of people, esp some who regularly read peer-reviewed papers, read over your paper is a good way to check for this.
Looking at judging rubrics and examples of successful papers for each competition you're entering would also help with this issue.