There is NO such thing as dual channel RAM and single channel RAM. There is ONLY, RAM.
ANY consumer RAM that is compatible with each other will run in dual channel if installed in a motherboard that supports it.
Buying in a matched set though, yes, that is a very good idea as it's guaranteed to work together. I wouldn't do it when you already have 8GB though.
It's probably worth at least trying to find another 8GB module that is the exact same part number as your current module, even though that is no guarantee they will play nice together. If you get a second module like you already have, and it does play nice with the other module, then it WILL run in dual channel in 99.99999% of cases.
If you want to get BETTER memory, in a 2x 8GB kit, then THAT would also make sense.