Oh my I can already feel the stress!!! No worries all blocks come with the size of it unfinished say 12.5 and the finished size is 12". One really easy block is the friendship star (really easy), rail fence, etc. are all nice in red, white and blue.
Here's a site for HST's that I found a while back. There are many many blocks that you can do with these.
http://www.blockcentral.com/a-halfsq...glepaper.shtml
Good Luck!!