Coopers is Australian. The reason I asked is that that Laagland extract is higher in non-fermentable sugars than other extracts, so you will end up with a higher gravity beer at the end of fermentation.
Anyway, You can add more yeast if you want, but my view on it is this:
are you trying to brew beer with a specific alcohol content, or beer that tastes good?
I strive for the latter, and I rarely ever use my hydrometer at all.
If the beer tastes good, I have won the battle, even if some software program tells me I didn't get optimal fermentation.