Hi,
I looked it up and basically your fine as your so far in, it is the the first twelve weeks that they think it can cause a problem something to do with sun light breaking down folic acid that is needed. The only thing they say at your stage is over heating and dehydration, so as long as when you got too hot you found shade, and drank loads both yesterday AND today your fine.
Here is a link to some info on it hope it helps to reassure you
https://www.babycentre.co.uk/pregnancy/isitsafeto/sunexpert/