I begin to worry because I have not received the parcel you sent me 2 weeks ago.
If I want to emphasize the anxiety that is growing each day, can I use I am beginning to worry ?
I begin to worry because I have not received the parcel you sent me 2 weeks ago.
If I want to emphasize the anxiety that is growing each day, can I use I am beginning to worry ?
I am beginning to worry is correct and natural, and it implies increasing anxiety, so the best choice for this context.
I begin to worry is bad grammar in this context because present simple implies a repeated event or a continuous state, but "begin" is not happening repeatedly, and is never a continuous state (something cannot continually begin).
I'm (getting) worried/It worries me (that) the parcel you sent me (2 weeks ago) hasn't arrived yet.
To stress the constant growth of your anxiety, you could use either "increasingly worried" or "more and more worried".
I am beginning to worry would be for present tense, and the past tense would be I began to worry