I hope you steeped the grains but boiled the hops. If you just steep the hops there is no need for separate additions. But to your question, the Cooper's can is probably hopped extract designed for no-boil brewing. Next time try a kit with unhopped extract. That way you can control the amount of bitterness by adjusting your bittering hop addition. Were the bittering units (IBU) listed on your kit? If so, go for something lower next time.
Alternatively, you could start drinking Imperial IPAs a lot. Then you won't mind the pale ale bittering range.