If you are managaing to do a law degree then being a check in agent wil be a piece of cake for you.
Stop worrying about it.
Its not a stressful job unless you make it one for yourself.
I see people get in a panic every day and then have to go and sort out their mistakes.
Remember ultimately all you are doing is getting people on a plane. The place would run a lot smoother if everybody remembered that and realised its not something to get stressed about and start panicing over, thats when mistakes get made.
Safety of yourself, the aircraft and the passengers is the most important thing. Dont ever compromise, or allow anybody to pressure you to compromise this, in favour of on time departures.
Keep calm and mistakes will be less likely to be made. I made one myself today because people were wittering in my ear and getting in a flap about bags and people not turning up and this that and the other and sent a pretty important telex incorrectly. I checked it out and resent it so it was no problem, but thats just an example of how easy it is to cause a mistake when people get in a flap.
Dont worry about your tests. Servisair have a pretty poor policy of nobody will fail them, so you'll get multiple attempts at it and pointed towards the answers anyway until you get them correct.
Take whatever training is being offered, take as much OT as you can do and always be on time and you'll be in a good position to be kept on i reckon.