"We are running fast."
Translation:Wir laufen schnell.
That's right. But in some regions of Germany they use "laufen" instead of "spazieren". Example: "I walk my dog"
I would say: "Ich gehe mit meinem Hund spazieren"
My friend say: "Ich gehe mit meinem Hund laufen"
"Ich gehe mit meinem Hund laufen" sounds to me like "I go jogging with my dog"
That's so confusing to me and I'm a native German speaker :D
You are trying to compose a present continuous with wir sind . Present continuous doesn't exist in German; they use another way to express continuity.
Google Translate is not always your best friend for a correct translation. If you had the sentence translated from English to German, you would have seen that your original German sentence was incorrect.
I don't know why wir rennen schnell is not accepted. Maybe because schnell is already suggested by rennen?