I have few doubts in the mgmat sc book. Please let me know whether the following sentences are correct.

1. What is the difference between the following two sentences.

Question : We are walking all over the countryside since last weekend.

I corrected it as

We have walked all over the countryside since last weekend.
< I believe this sentence emphasizes the continuing nature of the action which began in the past. The tense should be present perfect <have> + <Past Participle> >. I think this is correct

but, the following sentence was used to correct .
We have been walking all over the countryside since last weekend.

Please explain..

Thanks in advance !