Sounds like you should stay at the grocery store until a better Medical Laboratory Assistant job comes up.

You shouldn't stress yourself out financially, especially right now with everything that's going on economically in the world. Job security is something I'd personally keep. They'll be other Med Lab Assistant roles that come up. Just be patient :)

Alternatively, are you prepared to live on your boyfriend's wage and unemployment alone (worst case scenario) if you get no on-call shifts?

If this job is what you want to do for career progression, and you're happy to risk financial stability and having that extra cash flow a month because it's what you really want to do, then go for it!

With experience you could get a better role in 6-12 months (provided one comes up) that is more stable.

At the end of the day, do you want to risk financial stability?

Goodluck deciding :)