When you see a message saying "Mine too soon!" when trying to mine, this means that your system clock is out of sync.
To sync it up again, please right click on your system clock in the lower right corner of your screen (on Windows), and select "adjust date and time".
In the screen that opens now, please make sure the slider for "set time automatically" is set to "on" (right position)
This should remedy seeing this message while trying to mine.
Note: If you still see this message when you are trying to mine, please perform a malware and virus scan on your machine. It could be a sign of outdated drivers or malicious software running in the background.