Sorry - your question and explanation are rather confusing. I will try to make some corrections:
This sentence is in a story about my experience where I had a brush with death at a ski resort. What I'm going to say in the sentence is that when I got to the advanced course the first time, I mistakenly considered a road as a slope.
1. What I considered as an advanced course was just a 'way too real' course.
Additionally, I'd like to know a synonym for 'life-threatening'.
'course' is not such a good word to use. A course is usually either a course of tuition (i.e a class) or in sports it is a fixed track that you have to go along, such as the course for a race. At a skifield, you would only use the word course for a race course. A better word would be 'run' or 'trail' in the US.
Apart from your use of 'course' - part of the confusion for me is your use of 'road'. Did you really mean that you went down a road for cars, instead of a ski run? To me, that would usually not be 'too real', as most roads are much flatter than ski runs, so would be easier to ski than a ski run!
Life threatening: Potentially lethal. Potentially fatal.