Thank you all for the helpful replies. I do feel better now than I did earlier. I was feeling overwhelmed by the fact that a lot more is expected of me during my current placement than previously because it is my final one. I will be put in charge of the ward at some point and a big part of me was dreading that in case I made an arse of it.
I know for a fact that the university would not have allowed me to get this far if I wasn't capable, because it would reflect very badly on them if they sent an incompetent student to be responsible for the care of vulnerable people. However, an irrational part of my brain sometimed thinks I've fooled them into thinking I'm capable.