Megablast first marathon question

Hello,

My first marathon is coming up on 3/21 with goal of 3:50. I currently rotate between Novablast 5 and Superblast 2. I recently purchased a megablast which I was planning to break in next 3 weeks prior to the race but was slightly too long (about an inch gap). I can’t test it out because it is white color. My option is to reorder with half size small,or just use the new shoes or just use my old superblast with 270miles. What do you guys think?? Also when do you guys think the Asics will offer military discount to other color Megablast?