use of past continuous

Hi, can you tell me what difference would it make if I changed the part underlined to past tense? I think I don't fully understand the use of past continuous in a narrative situation like the one below and what difference the choice of choosing a past continous tense over a past tense would make.

What Joe did last year:

He went to XXX University in January.

He was planning to go to YYY University in February.

But instead, decided to stay in the same university.

Soon after, he was working (worked??) part-time in XXX Juice Bar in March,

But he gave that up after working one month in order to devote more time to his study.