Well, you are likely to still get a grade. Often in such cases the exam board simply deducts some marks (5% usually according to my Maths teacher), but it's completely up to them.
In the worst case they can choose to give you zero for that exam, but given you realized your mistake and didn't try to hide the calculator (which would seem far more malicious) it is extremely unlikely they will go that route.
Moderators don't hate you, if they think it was an accident they will try their best to prevent you from being affected too much.
EDIT: Apparently someone in my school did this with their C1 Maths Paper in 2014. They got a mark deduction of 10%, but given that the vast majority of questions on a C1 paper can be answered with absolutely no effort if allowed a calculator, this makes sense. In your case they will likely be more lenient, as I'm sure a calculator has rather limited use in a Computer Science paper