Got ABB yet most unis says courses are full and now have resorted to FY

Take a gap year and reapply? It might be helpful if you provided more information about what course you want to apply to, what subjects you're taking, and what grade you got in each subject.

Taking a foundation year isn't a bad thing if you don't meet the requirements for that course; you'll normally develop a good background in the necessary subject matter, and you'll also have a whole year to get used to the university before moving into the main course. You can also have as good an excuse as any to take part in freshers stuff twice, if you wanted (although you don't really need much of an excuse or a reason...).

Chemistry - A
Maths - B
Economics - B
Chemical Engineering, also applied to civil is which where I'm going. I love both civil and chemical engineering

Maths is very important in both chemical and civil engineering, as is physics (although that isn't always required). A foundation year would be a very good opportunity in your case to consolidate and expand your maths background, and begin developing the physics knowledge you need for those degrees. As above you also have the benefit of having the year to familiarise yourself with university life. A foundation year will also make no difference to your job prospects, and there is zero difference between someone who did a foundation year or who went straight into first year, either in academic or social realms.

As far as chemical vs civil engineering, this is something you need to decide on - a foundation year might give you an extra year to make a decision, and you would have ready access to the departments and academics to discuss the differences in that year. While they do cover some material which is shared between them (mostly thermofluids content), in civil you'll also do a lot of structural mechanics, strength of materials, geotechnics etc work, whereas in chemE you'll do a lot more advanced thermofluids work, as well as process engineering and reaction kinetics type stuff. In terms of job roles, while there is an intersection between them due to the similar content, there are a number of roles unique to each that the other wouldn't be able to do.

All in all, as above, I think for you, a foundation year would be a great choice, unless you are happy with the offer you have. I think you would get a large number of benefits from the foundation year, both in allowing you more time (potentially) to choose between civil and chemical engineering, improving your background in the relevant subjects to ensure you get a good result in your degree later on, and socially/personally to give you more time to settle into university life. As above if you don't go for that, your best bet would be to take a gap year and reapply; however I think the B in maths (and for civil engineering, lack of physics) might limit your choices somewhat anyway.