Are you using long tailed keywords or just a single word keyword? Better have lower keyword density for long tailed keywords.
Try these steps. When you write your contents, put your keywords couple times in the first paragraph. Than in the middle of the page, you need to mention them again. And at the end of the page, includes your keywords once again in the last paragraph. Note that you can only do this for every 500 to 600 characters long, because you don't want your site to look like a spam... Good Luck
Don't worry about the percentage of keyword density; just use your keywords naturally in all the places like title, h1/h2/h2, bold, italics, etc. Make sure you don't over do it and it should not appear as spam.
You should not attempt to put too many keywords in the articles content. The first and last paragraph should repeat the keywords 2 - 3 times.
Keyword density... Again... This is a myth. No ideal values. No real need to calculate the keyword density. It doesn't help if you have 7% or 70% - no difference. Search engines are far more smarter then they were when keyword density was invented and was used in search engine algorithms.