Should "nie martw się o odległośći" also be correct? Any reason why or why not?
Yes, it should be also correct. „Martw” is singular, while „martwcie” is plural. Many, if not all, plural imperatives are formed by adding -cie at the end of the singular form.
yes
it could be both
thanks
"nie martw się" is correct. but "odległości/odległość" has a spelling mistake, and odległości is plural
It is " nie martw sie o + accusative noun" .
"nie martw się odległością" should be accepted.
OK, added.