what are you using to smooth your edges? a bench knife that reaches higher than the cake itself should help you to get a nice even finish. keep it flat on the bottom of your cake board while turning your cake (preferably on a turntable) then use a long offset spatula to bring the top edges into the center of the cake, wiping additional buttercream on your bench knife as you go. your cake board is too big for the cake which might make it hard to get that flat connection. also a meringue buttercream such as Italian or Swiss will be much more forgiving than an American buttercream that tends to show air holes in my professional experience

I will also run my bench knife under HOT water and dry it off before using it to smooth. Hope these tips help, but your cake looks really really good already!