Did I over contribute to trad IRA / backdoor Roth?

I contributed $8000 to an IRA (I'm 50+) and the funds grew to $8300'ish - in December I moved all funds in the standard IRA account ($8300) to the Roth backdoor account.  I'm now doing my taxes, and TT is telling me there is an excess of 300 and a penalty involved.

 

Was I only supposed to transfer exactly $8000 from the traditional IRA into the Roth backdoor and leave the remaining balance ($300) in the standard IRA?

 

Thanks in advance...