TENSION: 21sts and 28 rows
Oh, I think I just solved my own problem. Was supposed to come out as 10cm on 5mm needles. And my piece is about 8.5cm x 13cm. But then I did 28 sts and 21 rows. Muppet.
I was wondering what one should do if ones tension is out completely in one direction and the opposite way in the other but I guess it's probably not too far wrong. Best knit another "square" just to be sure though