AI attempted my first SMBC tonight and it never thickened up. I used the recipe from sweetapolita and the meringue looked wonderful and had great peaks. Butter was not ice cold but also was not super soft. Not sure if it is because I tried to do 1.5 times the recipe. Any help would be appreciated

Honestly, half the time it is just a matter of letting it do its thing.  I could take anywhere from nearly instant to up to 15 minutes.

There are also two other ways of fixing SMBC.  If your butter was too cold, you can microwave a small portion of the SMBC in a bowl and mix that back in to the larger batch and let it come together.

If your mixture is too warm, just pop your whole mixing bowl in the fridge for 15-20 minutes then spin in around on your mixer again and let it come together.  I find this scenario most common because of still warm meringue.

Also Google the SMBC blog post from FromScratchSF.  It is an amazing educational tool and a great recipe to boot..

You could also give IMBC a try which to me is the lazier way of doing it.  Go to YouTube and look up Warren Brown's recipe.

I use Gretchen Price's- (Woodland Bakery Blog) and it works every time

IME it looks BAAAAAAAAAD before it comes together and looks perfect.  You just have to keep beating it.  You will think it's ruined, but just keep beating!