Guys dont worry , now I come with the clear information about crossing the red line only (not crossing the road and go other side).
In my case I crossed the red light line and I stop, I got flash and I did not reverse back, after the light turns green I move . I got a message after 6 days with photo on metrash with fine of 300 riyals only. If you pay within a month you have to pay only half that is 150 only. If you cross the red light and stop, either you reverse back or not the fine will be the same(the important thing is you are not blocking a vehicle)