Please tell me, why this sentence is wrong? I know the adverbs same/just/almost is come before verb, not always but in this sentence come before verb and this is wrong!!!
She just wants to take one class.
They almost drove six hundred miles.
Both are correct, but they may not mean what you intend to say.
They almost drove six hundred miles.
Means that they intended to get in a car and drive 600 miles, but someone called them and told them it was not necessary. They stayed home instead, but they came close to driving 600 miles (presumably for nothing).
They drove almost 600 miles.
This time they did drive. Not a full 600 miles, but almost 600.
So almost refers to two different things in these phrases: "They almost drove" (600 miles), versus "almost 600 miles" (they drove).
She just wanted to take one class.
She didn't want to organize a school party, upset the students, set the school on fire; the only thing she wanted was take a class.
She wanted to take just one class.
She didn't want to take 2 classes, or 20. Just one.
So, although your phrases are not incorrect, placement of the adverb changes their meaning.