To be honest, yes, you really do need to get it checked out and if they don't know that you've been purging then it's unlikely to be obvious to them that that's the cause; I've scratched my hand on many things before and that could've been put down to purging if I thought of that but it was through one of my many accidents back then. Really, it's likely to be more that the acid going over the area after the initial scratch that has caused it to worsen.
You do need to dress this area as good as possible, cut a normal dressing so that it will fit over the area but you can still move your hand, or try and do that; you may find it hard and using multiple dressings may be the answer. Use non-stick ones with either adhesive edges which may stay on better or holding them in place with medical tape, or even better, a bandage wrapped around your hand. Before you apply the dressings you need to clean the area as good as possible, trying to make sure that it is clean and also apply antiseptic cream to the underside of the dressings. Really I think this is better being checked out. Not just because of the possibility of infection, but also because of the fact that it sounds like it covers a large area and as that heals the scarring has the potential to be quite bad and so tighten up the skin in the area and so it should get checked out; best would be to get checked over the weekend and as you live in Wales then phoning your normal surgery and if they're open in the morning then booking an appointment with a doctor/ nurse there, or if they're not, then on their answerphone should be the details of how to get in contact with their out of hours provider if it isn't themselves that does the out of hours work.
Really it would also be a good idea to mention to your doctor about you ED so you can get support from it and they can help you to get out of this which is really dangerous and get you the support that you need and though this is scary, the sooner you do that, the better in terms of your health but also your emotional state. If you're scared to tell them you could always write it down or take a friend with you who knows.
Though, if you're not ready for them to know then there is no reason really for them to jump between damage to the skin on your hand and that being due to purging. I think it may also be worthwhile for you to read the
First Aid ED Article.
