the disk you inserted was not readable by this computer

I have been using a Lexar USB for a while with no problems. I shut down my computer and when I powered back up and inserted my disk i received this error. I removed and inserted disk many times and received the same message. I did also click all of the options, eject, ignore and initialize at some point. I went to disk utility and did the first aid option and it failed. It appears that the data is still there because it is showing as fully used to capacity of 16GB, but I am not sure if that is correct. I am scared to do the restore option because I don't know if it will completely erase all of the data. Please help. I have been reading options on internet for hours. I can't afford to lose my data. I have MacBook air Sierra OS 10.12.3 thank you in advance to anybody who can help.