I filed my taxes in California and missed $150 of interest income. I received the full refund calculated which is greater than the revised refund. What should I do?

You need to amend your return and pay back the difference.

How to Amend this year

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-federal-tax-return-current-year/L7eS6o1qh_US_en_US

You will still get the refund from the first original return or still need to pay the first tax due.  In fact you should not even amend until the first return has fully processed and you get the first refund or your tax due payment has cleared.  

Then the amended 1040X return is only for the difference you get back or owe.  I think the cover sheet shows what the original return WOULD have been if you did it right the first time.  Ignore the new 1040 that might print out.

Go by the actual 1040X.  Line 18 should be your original refund amount and line 22 should be your additional refund.  If you paid on your original return it will be on line 16.  If there is an amount owed with the amendment, it will be on line 20.

If you have a tax due, do not send the 1040V.  Just include a check with the 1040X.  Ignore the 1040V.  That is for the original return or what the original return would have been if it didn’t need correcting.  Don’t pay the amount on the 1040V.  Pay the amount on the actual 1040X line 20.

Or You can pay the IRS directly at

Https://www.irs.gov/payments

I don't think CA will go after you for the tax on $150.

Although I hear it is a high tax state.

File an amended CA return and remit the difference to the CA FTB.   How do I amend my CA state tax return?