So, it won't be impossible for you to catch up and with everyone in the same boat, I recommend you use online resources to try and keep up to date with where you should be in your course. Grade boundaries will most likely be lower with everyone performing poorly in areas that should've been taught over this time. You should not be disadvantaged, many schools are running online classes if yours is not for whatever reason, use your textbooks or your online resources. Your teachers will also know where you left off and this will most likely be covered in the start of your second year or looked back on in revision sessions.