How can I duplicate and mirror a designh made of

Hi all!
After a few years of repaints I thought it was time to try build my own aircraft but as a beginer I face a few problems.I made a desighn of the aircraft left side top view and now I want to select all the lines duplicate them mirror and paste them in order the to view to be symetrical.The problem is that when I tried to use the select tool it didn't select all the lines.Can anyone sugest something???Even a tutorial sugestion is more than welcome :)
Thanks or your time!!
mirrage
After a few years of repaints I thought it was time to try build my own aircraft but as a beginer I face a few problems.I made a desighn of the aircraft left side top view and now I want to select all the lines duplicate them mirror and paste them in order the to view to be symetrical.The problem is that when I tried to use the select tool it didn't select all the lines.Can anyone sugest something???Even a tutorial sugestion is more than welcome :)
Thanks or your time!!
mirrage