KIT says

[iammeegan]

Does anyone know whether you can do more than 10 kit days or is that a set amount also if you do more how much maternity pay would I lose?

No you can't. If you do more it would stop your maternity pay

I've found this online:

Once you have worked for more than ten KIT days/20 SPLIT days you will lose a week’s SMP/SAP or ShPP for any week in which you do some work, even if it’s only for one day.If a week contains, for example, the last of the ten KIT days and another (eleventh) day of work during your maternity leave, you will lose that week’s SMP/SAP. However, you are still entitled to any contractual pay that has been agreed for your KIT days.

From www.maternityaction.org.uk/advice-2/mums-dads-scenarios/pregnant/keeping-in-touch-days/