You would be making a 6" block, 4-7/8"" hst for center, and cut 20 each (measuring 1-7/8") squares of 2 colors.
The block is called Lady of the Lake. Here is a link to a 10" block at
http://www.quilterscache.com/L/LadyoftheLakeBlock.html
If you want to use your 5" charm pieces this block size is too big, you have to stay with a 6" block. This shows you how to piece the block.
Good luck