You will be ok, it's good that the owner knows, that will help 
Remember to breathe, and don't listen too hard to instructions. That sounds strange, but you will take in more if you don't try and focus on every little thing. Also, you are not the centre of attention, though it feels like that sometimes. People are just getting on with their stuff though, they are not that bothered with what you are doing. That can help relieve pressure. You will be great st your job in a bit of time, but dont feel you have to everything all at once. 
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Nothing lasts but nothing is lost