Today I am going to write a little bit about my day; how it was, what I did and stuff like that.
I left home about 4 am (prefferably 4 AM), it was a really hot morning and I mean hot (it)!
(I preffer "and I mean hot" or "and I say hot")
Until then, I woud hardly know that the day would be much hotter.
In the morning I took an exam at my/the university. I thought I would have a hard time because I hadn't studied enough to be confident. Thank God it ended up being an easy test/an easy one. The things I had learned were in the test.
I see that you got a bit trepidant to write "cairam na prova" (were in the test), but you were right, go ahead.
Your writing is going from strenght to strenght, congrats.