I hope you find the corrections useful.  Feel free to message me in case you need me to explain the corrections in detail.

I agree that you are in a difficult situation.  At this time, I think you aren't confident yet about your proficiency.  I agree that you still need to improve, but what will make your struggles less painful is your confidence in yourself. They chose you for a reason!  You may have the skills that they so require.  You can always find people who could help or online materials to polish your English skills.

Good luck!

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I have to make a confession.

Today is (was) my first day at this in a new job. But I am (was) a little worried about my English speaking skills (skills speaking english). The job requieres a certain level of knowledge about this language(lenguage) (English) because I am going to (gonna) have to report some activities and results here in Mexico to the global team at England.
I was hired a few days ago, but I (i) feel like I lied (a lie) about my level of English, that I (i) think it's not good enough and I'm a little terrified.
In the past days I've been studying: making excercises and reviewing (repassing) all that I know, but yet I feel kind of insecure (yet).
Thank you for reading this write up.  It makes release some of my worries (concern).

I have a confession to make.

Today was the first day of my new job. I was a little worried about my English speaking skills.
This job requires a certain level of knowledge about English, because I am going to have to report some activities and results here in Mexico to the global team in England.

I was hired a few days ago, but I feel like I lied about my level of English.  I think it's not good enough, and I'm a little terrified. These past days, I've been studying, doing excercises, and reviewing all that I know, but I still feel kind of insecure. 

Thank you for read this. Writing it helped release some of my worries.