Sometimes the harder you try the worse it gets?
You clearly have a desire to undertake the role of a social worker but probably begin to appreciate the huge demands of professionalism placed upon you. If you are finding it difficult now within a supportive environment it is only likely to get worse? If you are expecting an assessment for ADHD as a reason for your inability to reach key targets then your performance is unlikely to improve right now and may possibly not improve in the longer term going forward.
Considering another job in a less demanding career might have to be an option for you? I would seek some professional medical advice and ask about the current medication regimes open to you to treat your mental health issues, and if they think this may help you in any way?
You definitely need to speak to your tutors and course administration department to see what they think your options might be? You may be able to switch courses early on? Alternately they might have opportunities for you to take a year out to stabilise your condition? Only you know how out of your depth you are finding yourself and whether this career is the best career for you?
Try if you can to look at everything pragmatically. If you decide not to continue it takes a whole lot of courage to face that and make that decision. Take credit for that. You will have learned a lot about yourself too. Life is a series of uphills and downhill sections in the Grand National of the life track. As one door closes another suddenly opens. You could have an amazing career in a field you haven't yet chosen, and this could all be down to the fact you left Social Work. List all the positives for leaving the that difficult profession.
Then after chatting to your tutors, your GP, any specialists you can formulate a plan of action. If you decide to keep going, be determined. You should make a list of areas you really want to change, a plan of how you can change and if that is realistic? Well done for having a good hard look at all aspects of this. Your placement may be a minor part of your course, but that depends on your evaluations of the year and the terms and conditions of your course. Do your best, nothing more. I hope you can succeed with encouragement and if appropriate, good medication. If you don't succeed, this is still a layer of life with friends, contacts and life experience. Good luck either way.