Outrageous public indecency?

Im 18, Me and my bf were in a ikea car park and got a bit carried away, reclined the seat and were snogging. Security guards saw and banned us and reported us to the police.

We went to the station today and they said I will have to come back tomorrow for an interview tomorrow and to bring legal aid. They couldn't say what the outcome would be e.g CPS prosecution for outraging public indecency or caution etc
Later on they rang to say action they still want to see us tomorrow but for a written warning with no caution and won't go on the record.

My question is what is a written warning? Does it go on my criminal record? I read online that it is a caution?? What happens if I accepted the caution? I know it would show on an enhanced dbs check but I plan on applying a healthcare course working with vulnerable people- these courses are exempt from the rehabilitation act and I will have to declare all spent and unspent convictions. A caution is spent. Will it affect my ability to get onto the course and will a caution impede my ability to work in the healthcare profession with it on my DBS.

I feel like what we did wasnt that bad but from the sounds of it it sounded like it wasn't a proper caution but it's written?? If It was a caution and I refused to sign would I be arrested and taken to court?

I have called a soliciter and they will be coming tomorrow to the station. HELP