Dont worry, you can put in your personal statement that you have work experience coming up, so ring back the hospital and request that they book you in for january. In the meantime call up other hospitals and see what they have available. Volunteering at a care home is good, likewise the week at the vets. Other things i would suggest are see if there are any youth organisations that could arrange for you to help out with people who have disabilities, its a valuable experience and it gives you a greater understanding of the type of disabilites people can have and how it affects them and their families. You could also try dentist surgeries as they have to deal with medical conditions as well as more cosmetic procedures.