have you had previous funding from student finance? If so they will only fund limited years of study.
You can apply for the extra year of funding but this will only be granted in exceptional circumstances. For example bereavement, mental illness etc, you will also need evidence to support it.
Have you already received an unconditional offer for uni?
In this case you need to contact the uni as soon as possible and explain your situation. You will most likely need to defer your place until year and save up to fund that first year. You'll then receive student finance for the remaining two years.
Hope this helps