I am worrying vs I worry

Hi.

I use „Grammarway“ textbook series to review grammar. And in „Grammarway 2“ on page 12 (in case you have it) there is an exercise where you are supposed to put the verbs in brackets into the present continuous or simple. It is a letter, where the writer is writing to his friend. He mentions his summer job, so it is a temporary job, his working hours..... And then it goes like this:

„I am working (work) very hard at the moment. To tell you the truth, I am (be) a bit nervous because my boss is leaving (leave) for Scotland for business new week, so I'll be on my own. Lizzie says I ____________ (worry) about it too much. She's probably right!“

What are your thoughts? "I am worrying" or "I worry"? The key says „I worry“. I would prefer „I am worrying“.

Thanks for your thoughts.

Radovan