I don't think it's too late to return the SM300... You have 2weeks unless it's already lost some 'unworn' conditioning...
This whole thing is so upsetting...
whole boutique model functions on the idea that the watches are emotional objects...and they aim to create a point of sale experience that will transcend any discounts you could get elsewhere...
I Wouldn't play 'hardball' and threaten, but I would leave the sm300 unworn... And give the manager a chance to help make your AT whole... If He can't/won't, then Id explain that the SM now has negative emotion attached to it, and it would affect your enjoyment of it over the years if you had to think about the aquaterra every time you looked at it...
(A little dramatic, but also using their side of the argument... Could they really argue against you feeling emotional about a watch?)
I'm the first one to say that the discounts elsewhere don't make up for Boutique experience ... But when the experience is negative its a different story...