lightly brush some oil on the bottom AND the sides of the pan....doing this usually keeps my brownies nice and moist along the edges.
the brownies are done when the top part starts to crack a little. Also you can touch it from the top.....if it feels spongy (bounces back up) then it is ready. Another method would be to stick a tooth pick in it....if it comes out clean then it is ready.
be sure to check which rack you put the brownies on....if it's too close to the heat element then it will overbake. place the brownies on the middle rack.
when your mixture is not evenly spread and you have more mixture in the middle and less on the sides then they get little harder on the sides. Maybe next time use 1 size smaller baking dish...