Can anyone tell me if I have done this right.

Because the store was closed.

my answer: Because the store was closed, we went back home without the food.

I think you did it correctly. I am not sure what the teacher was asking for.

But you took an incomplete sentence and made it make sense.

Matt

Yes, Matt's right. You took a sentence fragment (incomplete; subordinate/dependent clause) and made it into a complete sentence by adding an independent clause.

=)

well I am trying to see if I use the correct Punctuating Sentences

The punctuation is also correct - GOOD JOB>