constructive criticism? Before you scale something up, don't.
Is this piece for commercial use? Uni? Portfolio?
Because if it is the later, there are loads of stock sites that will have something similar to the elements you need that are free to download and will be high enough res that you can use them in A2 300dpi files, I know, I've used them!
You have something alright going on, but the pixelated detail is a total no go. It will make your work look 2nd rate.
Just make that line color more lightning its pretty amazing already. it depends for what purpose is this poster... if is "person garbage", dont get me wrong i just talk that way, you can make many changes you want because the only purpose is making this poster visual and pretty cool. if there is some porpuse you need to tell us and focus on that. Imagine that this poster is for tell him old people like my grand mother that they need to make exercise ?!!!? that poster would be fun and ridiculous