Having been involved in recruiting for a UAS I can tell you that the process at Freshers Fair is pretty hit and miss: until you get to the formal, structured process you won't really be subject to an objective assessment.
The chat at Freshers is designed to weed out those candidates who are patently unsuitable: regrettably the shiny keen "I was a CWO" is probably less likely to be selected as they do present themselves, and this is no reflection on you as an individual, as immature, lacking exposure to the big wide world.
The subject of your degree is irrelevant: a balance between the arts, sciences and humanities is always needed and AT Management would not prejudice your application.
The advice about getting out and about and broadening your experience is first rate: join a couple of clubs / societies at Uni and network.
Don't give up or become disheartened: don't distance yourself from your ATC experiences but use them as the building blocks to step up from.