Much like the USA flag, the CSA added stars to their flag as they new states joined - from the former 7 to 11. However, eventually up to 13 stars were added (because both sides claimed Missouri and Kentucky as own).
In actuality, there were multiple versions of this flag. Examples on file include those with a single star as well as these star counts - 4, 7, 8, 9, 10, 11, 12, 13 , 15 and even 17!
Source: «Historical Flags of our Ancestors» website: Flags of the American Civil War.
Sizes: ensign W11 x L18 mm, mast flags W8 x L13 mm, jack W6 x L9 mm, pennant W4 x L48 mm.