Homebrew PCBs

I am trying to produce a small PCB for a SMD pic16f628a-i/so using 
chinese blue dry film photoresist. The exposure seems to work fine using 
a bank of uv leds and the photoresist turns a nice darkish blue around 
30-45 secs of exposure. I am trying to develop using washing soda (I 
forget the exact strength but I think it was 200g in  litre of water). I 
am having difficulty getting this process right. Either some of the 
unexposed photoresist does not come off (particularly between close 
tracks) or some of the exposed photoresist lifts if I leave it longer. 
Anyone having experience with this process willing to comment on what I 
may be missing.