You should be seeing a very bright image with your current cable.
I do not when I use the OSSC. If I take the scart directly to my TV/monitor (an old Samsung that has both scart and DVI and VGA) then the picture is rather bright.
Therefore, the resistors could very well be to small. There are reports of people using 220R resistors with good result. I will give that a go and see if that changes things :-).