The PGCE FE is near-worthless. It doesn't offer QTS and therefore won't qualify you to teach in a school. There is no "top up" qualification to turn your FE PGCE into a 'proper' one so the only option you have is to do a whole new PGCE (but a secondary one). This will cost time and take at least a year to complete. Technically speaking, a school COULD still employ you to teach maths with your FE PGCE but you would be on an unqualified teacher's pay spine.