You don't have to do that, even if you did the ritual imperfectly it still works. Nobody really does 100% perfect, it's impossible.
I'll tell you the real reason many people want to do it again: they feel it didn't work because they didn't experience anything out of the ordinary during the first time. If you are not astrally open, then if you do it correctly you will not experience anything extraordinary. I am one of those people who did the dedication 3 times because I thought it didn't work because I didn't get enough blood and the justification for it is that I didn't experience anything. Not in a single one of those 2 additional times did I experience anything.
In the dedication ritual, it's mostly your intention that matters.