My control number on my W-2 is just 7. It says there should be a minimum of 2 alpha or numeric characters. What do I put?

Don't import your W-2, you only need the control number to import it.   Enter it manually and leave the control number box blank.  

NOTE:

Oops!   I didn't notice that @DawnC  had already answered this question.  I saw that right after I posted.

Sorry for the duplicate.

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Are you referring to a Box D control number?   If so, it's not required by the IRS. It's a number used by your payroll department.  You could try just leaving it blank.  If a blank Box D produces an error, you can try making up a number in the format shown in this FAQ:

https://ttlc.intuit.com/turbotax-support/en-us/help-article/import-export-data-files/box-control-number-w-2/L8MD2FqqP_US_en_US