Suggestions for corrections to your text:
The letter that changed my life
It was a rainy evening. I had been working hard all day. All I wanted was to get home, have a warm shower, and eat a hearty dinner. I drove home, as quickly as I could, and *regardless of the heavy traffic, I **managed to arrive home ***half an hour later.
Before going/entering into my house, I checked the letter box to see if any letter arrived. There were a pack of bills, as usual, and a different envelope amongst them. I opened it, and there was a letter saying/stating (or you can say: the words written were these):
We are delighted to inform you that you have won a fortnight trip to Italy with all expenses paid by our tourism company. It’s a trip for two, so you are allowed to bring a friend.
The departure is next Friday at Guarulhos airport. All the procedures and relevant information will be sent to you by email as soon as you confirm you are willing to go.”
Global Tours manager
After reading the letter, I invited one of my best friends, Maria Joaquina. She accepted my invitation at once and very shortly we packed and took all the necessary procedures to take a trip like that.
We landed in Rome five days later. We went sightseeing every day, ate in great restaurants, visited museums and went shopping. We, also, had the chance to visit Florence and stayed there for three days. It was a marvellous and very enriching experience and, for some time, I was able/could forget my tedious and unappealing life.
This letter changed my life because, at that time, I was going through a very difficult situation in my life which brought me a lot of uneasiness and sadness. The trip to Italy was everything I needed to relieve my suffering.
* "Despite" is right too, but "regardless" makes it easier to understand.
** You can say "to be able to", but "manage" is more common, in this context.
*** "Thirty minutes" is technically correct, but, in this context, "half an hour" is a lot more common.
Ana, you are a good writer, and the way you do it is very suitable to write novels. I look forward to your book launch one day.