You could use these expressions instead:
\w– is the same as[a-zA-Z0-9_]\d– is the same as[0-9]\.– is the same as[.]{1}
Which would make your regex:
^[\w,\s-]+\.[A-Za-z]{3}$
Note that a literal dash in a character class must be first or last or escaped (I put it last), but you put it in the middle, which incorrectly becomes a range.
Notice that the last [a-zA-Z] can not be replaced by \w because \w includes the underscore character and digits.
EDITED: @tomasz is right! \w == [a-zA-Z0-9_] (confirmed here), so I altered my answer to remove the unnecessary \d from the first character class.