We are not "superman", and cannot do everything there is to do at once. The unknown can be scarey for sure - but what is "unknown" right now? Why would your boss give you work to do that you don't know how to do - or could it be that with your anxiety high, you just dont give yourself credit for really knowing how to do it?

Remember to breathe.........and when I owned a store, I found "most" customers were OK if I was a little slow getting to them, with a simple "I have just a few seconds to finish this order - be right with you". Being a small store - I did not want to lose business - but at the same time, I knew I had to not become overwhelmed - which is sounds like you are now. Hang in there - the day is more than 1/2 over !