How to ask crush out?

Hi,
I am 28M and the girl is about 25 years old.
Long story short, next week is our last week working together as our contract is ending. We do talk whenever we see each but haven’t really talked about our personal life. I really like her, her work ethic attracts me! I do have her phone number because she was added to the whatsapp group by another colleague.

She is always with her group and it is really hard to talk to her! It’s killing me. Saturday will be our last day.

What should I do? Should I just text her on Saturday?
How to ask crush out?
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