1. You can go and see your student advisor at the SU.
2.
https://www.rcn.org.uk/get-help/rcn-advice/investigationsContact the RCN helpline.
0345 772 6100.
https://www.rcn.org.uk/get-help/legal-helpThis is assuming you are a student member.
3. Imo you need to take this very seriously. Do 1 as at least you can get it off your chest and have someone listen.
You have 2 options.
i) Deny it or make up some story about paying bit it was closed and you were looking for somewhere to hand in the money etc. This would ofc be untrue and unless it was watertight the continued lying would create more trouble than the considerable amount you are already in.
You could only use this if your story was rock solid. As you werent even aware enough top notice the security guard I do not think this is an option and there are a couple of ways they can almost certainly prove you stole. You may also be on cctv or he obviously observed enough. You werent careful enough.
ii) Tell the truth and be contrite. You have to present this very carefully as a one off, not thinking, ashamed, grovel, realise your whole career is at stake. You are seeking to avoid them kicking you out. Maybe you had some depression or things going off at home?
You let yourself and the uni down, never done anything like it before etc, character references.
Nursing depends on you being a professional and part of that is about your honesty and integrity.
What happens if you lie to your colleagues? Someone could die?
What happens if you steal from patients or rugs from the NHS?
You made a bad decision under no pressure.
Do not lie, take it seriously, but do protect your interests and dont go over the top in apologising and making it seem worse but dont be in denial.
Ask them for another chance.
You are at very serious risk of being withdrawn due to dishonesty, for the sake of £1 and a very stupid decision. If you are then you are going to have to notch it down to experience and learn from it.