The nozzle won't be a problem in that it's runny, but it just won't give the same shape as the Wilton 1M. It's still perfectly use-able though, just don't expect the icing to look the same as the other cupcakes on here.
As for how runny it is, try to use butter from a pack rather than spreadable butter, it will set harder than spreadable. If using anything liquid, be it flavouring or colouring, you'll need to use more icing sugar (as you have done) to get it to firm up. Try the different butter, hope you'll get on better as the cupcakes do look yummy!