I'm really surprised it says that, as many of us would consider 21C on the high side for an ale yeast let alone a true lager yeast e.g. I've got a Coopers Stout sat at a nice cozy 20C at the moment. I normally brew Coopers European mid-winter after Xmas as that's when the house temps are at their lowest, have a feeling the instructions I read said a temp range of 8-16C for best results but of course they went in the bin 6 months ago. They may have changed the instructions too.
It'll probably be fine. Most ale kits and lager kits (such as Coopers Australian) use ale yeasts which work best 18-24C (I usually aim for 20), a few kits use a lager yeast which works best at cooler temps.
And if you want to make it even better, get some Hallertau or Saaz hops from your local shop or eBay (15-20g should do), chuck them in after 5 days of fermenting and leave them there until you bottle / keg. Oh, and don't follow the "it'll be done in 5 days" or whatever instrcutions, leave it a good 14 days at least and only move it when it starts to clear. :thumb: