No problem. Think of it this way: if it's good, does it matter how long it is? Another idea is that you could write every other day and use that extra day to research more. It really depends on what you want to tell / show people. It seems to me like you're just telling how it is (and in this year that happened, and in that year this happened) and while there are things you can learn from that, it doesn't put the ideas on the first place.
Think about what goal you want to have with the blog besides writing it up. If you want to focus on a historical account of flags, maybe think of the role and context that lead to the creation of this flag. Congress wanted a new flag, why did they want that, and does it make sense in historical context? If you're more into design / symbology, maybe you could write something about the color use, the placement of the stars, why they chose stars etc. You know your field better than I do.
In the end, all we have is perspective.