Claire,
You'll on a difficult regime to do corrections, as if you correct with using mixed insulin you are also adding in more background insulin not good, really need a quick acting insulin only..
As to what point to call the medics, sooner rather than later, if you feel unwell then give them a call or pop down A&E, that's what they are there for..
They may give you some quick acting insulin, so you can correct without faffing up your background insulin and some ketone sticks if you haven't got any so that you can monitor your ketone levels..
Take care and never worry about calling the medics