Graphic Resolution

Good morning...

I had a friend create a graphic in illustrator to put on a custom flag I am wanting made. I've tried multiple uploads, to two different custom flag making websites and each time they are telling me the graphic's resolution is not good enough. Obvisouly I don't want to print something that is going to be blurry. 

This was going onto a 2'x3' flag. 

I am not versed in Illustrator at all. I have the suite becuase mu job requred some of the other programs. Could anyone tell me what I can do to this file to make the resolution better to be able to print onto this flag that is that large? I'd be happy to email if needed. It is too large to post here. 

Thanks!