Generally speaking you should avoid mixing different coolant formulations (usually indicated by different colors), as that decreases the overall lifetime of the coolant.
Seeing as you've already added it though, I wouldn't worry about it. I doubt there'd be any seriously harmful effects (ie precipitates, etc).
For the future, get yourself a jug of
Subaru Super Coolant (blue in color). Best price when I bought it was on Amazon.