Hi, as a Brit and mentor, but not a teacher, I would advise as follows:
Your text sounds like an extract from a mystery thriller, with, initially, short punchy statements (mainly) in the present tense, giving a sense of immediacy. It then switches to the past, when the need for immediacy is over.
It's pouring [/raining] outside. (i.e "It's pouring", "It's raining" or even "It's pouring with rain") I forgot to bring an umbrella (even though this last sentance is in the past tense, it reflects your immediate problem).
The streets in Shaw town are not very clear on the map and I am afraid I've got lost. Now, I've got soaked and don't know where to go.
I ran [run?] (you've switched to the past tense for this paragraph - intentionally?) to the nearest bus stop. I took [take?] shelter under a roof at the front of a department building, waiting for the bus.
Luckily, bus came (this is where I would have switched to the past, as you are closing out the immediacy of the situation) soon. I got on and went home.
Hope this helps
Student or Learner