I was presented with the following sentence and am wondering if this is formed correctly. I had learned that you should not mix tenses but in this case it is using past (albeit preterite and imperfect).
No creo que hice lo mejor que pudiera hacer.
I was reading about the past perfect subjunctive forms and am also wondering if it would make sense to form it as the following or are they effectively similar?
No creo que lo hubiera hecho mejor.
It seems that the subjunctive is warranted simply because "no creo" but I struggle with these sorts of constructions. Am I nitpicking or is this slightly off?