I'm fairly new as well and have had this issue.
It will flag and it will make you nervous to start with but hubpages admin does not want to be contacted to say it is yours on another site, this hopefully makes it ok. This is what the flag says:
NOTE: A substantial portion of the content on this hub appears on other sites
This Hub seems to contain text that also appears on another site, and may be incurring a HubScore penalty as a result. If you revise the content so that it is unique to HubPages, your Hub will automatically be rechecked for duplication.
The issue of duplicate content on HubPages is completely separate from issues of plagiarism or copyright. All that it means is that we found text very similar to what is contained in this Hub elsewhere on the Web. Promotional or affiliate links are strictly prohibited on Hubs identified as duplicate.
Please do not contact us to say that this is your original content that is published on another site. However, if you believe that this content should not appear anywhere else on the Internet, please contact us. Include the URL or title of this Hub in your message."