First off, thanks to Greenwoodrover!
I didn't get the water all the way up to boiling point, but managed to get it to the right temp and it worked perfectly; hit my target post-boil SG spot on
Thanks to everyone else that gave advice - trubadour I do use brewsmith but only had my mac laptop with me and beersmith is on my work pc upstairs so I was in a bit of a panic.
The reason why I missed my temp is I knocked the strainer off whilst stirring the mash in and had to empty the tun into a pot and then pour it back in!! such a disaster but it turned out ok : )