To tense, or not to tense?

My biggest problem with my stories is maintaining the same tense throughout. One of the thing I will be doing this week is searching my manuscript for words like ‘is,’ ‘has,’ etc…

Because Josephine Marlin and the Alternatives is told from a first person point of view (POV), I am telling a story from my protagonists perspective therefore I need to maintain consistency with my tenses.

This is the tense I am writing in, past.

She knew she had to get to the store before Monday, but the car broke down and the mechanic said it will take a week to have it fixed. She called her sister to take her instead.

This is the present tense:

She knows she has to get to the store before Monday, but the car broke down and the mechanic say’s it will take a week to have it fixed. She calls her sister to take her instead.

My writing is in the past tense but some of my story is a batch of mixed tenses:

She knows she has to get to the store before Monday, but the car broke down and the mechanic said it will take a week to have it fixed. She called her sister to take her instead.