Translation:That big intersection is a little dangerous.
They are 2 words of the same meaning. 大きな follows な type rules and 大きい follows い type rules. Usually for tangible things we use 大きい, and for conceptual things 大きな. However there's large overlapping and it depends on the intention of the expression.
So don't worry about it too much. The only thing that needs to be remembered is not to use 大きな as a predicate. Saying 大きなりんごです is not wrong, but りんごが大きなです is definitely wrong.
Your idea would work if the word were すこしい, however the word is actually spelled すこし and so follows different rules.