Drumshanty - I think most of the answer to your question lies in the opening remark "I rarely sing ballads". Remember that a competition is an artificial situation anyway, so to tackle a ballad that you don't sing frequently is to put yourself under undue pressure. Pip Radish offered good advice, to practise a lot, and I would also suggest that choosing the right ballad is very important.
If you're fearful that it's too long, then try to find a shorter version; if you worry that it might be dragging, then consider learning one of the more rhythmic or pacy ballads like 'The Wee Toon Clerk'; and if you don't love, don't do it!
Remember too that people you may hear who sing ballads impressively now, were probably just as beset by doubt as yourself when they first started. And also bear in mind that most of these same people would be happy to talk ballads with you, and perhaps offer you some tips about what works for them.
There's some great advice on this forum, from the points of view of both novices and more experienced singers -- but the best advice is to keep doing it!