Do you mean Maternity Allowance? You do have to inform DwP about Keeping In Touch days, but they won't affect your MA at all as long as you work on no more than 10 days - that is the whole point of KIT days. If in fact you are employed and are receiving SMP then it is unlikely that work you do for that employer would be seen as self employment.
Should be OK so long as the bulk ( all bar your 2 KIT days) of the work was undertaken before you started claiming Maternity Allowance.. I'd make sure your invoice has dates ( or period of dates) that precede your MA dates.
ie- services supplied between Jan 13 and April 13 on X project.
I've got a thread about KIT days on MA at the moment too - it says on the MA1 claim form you have to tell 'the jobcentre plus' but nobody can tell me how to do this, I've googled like mad and aparently nobody at the Jobcentre Plus really seems to know anything about MA for the self-employed.
Some people on a zombie thread I found from 2010 said they were just asked for the dates at the end when they wrote to cancel their MA.