気にしないで、大丈夫だからって英語でなんて言うの？

1. 'I'm good, really!' - This is telling your friends, that hey listen I'm good right now, even if they think something is wrong I'm telling you 'Really (actually, truly)' that I am good. Saying really after is like telling them to trust you and not push you for more details.

   2. 'It'll be ok, I got this' - This is encouraging the people around you to trust that you understand the situation and everything will be ok because you know how to handle the situation.

   3. 'Don't worry, it's all going to work out.' - Here's another way of saying that you will figure everything out and that no one needs to worry about you or the situation you might be in.

Sometimes one finds oneself in a bad situation and friends and relatives begin to get bothered. They may come to the person and try to console him/her. Seeing that all these people are worried about his/her difficulties, one may be compelled to console them back. Using the phrase 'no need to worry' is the same as saying 'there is no need to worry'. The verb to "bother" used in the third sentence is just the same as 'worry'.
So, you may say:
No need to worry about me, I'm fine.
or
Please don't worry about me, I'm doing just fine.
or
Don't let my issues bother you, I'm OK.

Sometimes we feel let down and those who care about us can feel our pain with us, when people care for you, they will apologize when things don't seem to go the way you would have liked.
To let others know that you are fine and they shouldn't worry, the sentences above can be used.

Fret: worrying a lot
Concerned: worried

"Don't fret about me, I'm just fine."
"There is no need to be concerned about me, I am fine."

The first phrase by saying you fine is another way of saying that you are ok.
The second phrase is another good way of telling someone not to worry and that although right now things aren't going as you hoped they will be ok.

If things are not going as well as you would want and your friends are worried about you and are enquiring about you - but you are OK, then you may use one of the abovementioned example sentences. The second is more formal than the first.

"Everything is fine!" is a very casual term used, explaining that everything infact is good and there are no problems.
"It's no biggie"
'No biggie' is a term used to describe that it is not a big deal, its not a problem and that you shouldn't worry or be scared.

either of these sample sentences should let your friend know that there is nothing to worry about

When you find yourself being asked many times by friends or family if you're okay and don't want to be impolite, you may use these phrases. By ending the phrase with "thank you" gives a friendlier tone of what you are saying.