Is it okay to use mainly websites as resources for my assignment?
No. At university level, you are expected to use only credible (trustworthy) academic resources. These include books and journal articles.
Websites that are considered credible are government and education websites. You can easily identify these by looking at their url. They end with .gov and .edu.
If you are using websites, ensure that they are in addition to the required number of credible sources. Always check with your Learning Facilitator first.