No matter what you do, you will always be "doing your best" because time is linear and you will always have done however well you did. If you could have done better you would have, because "your best" is dependant on you as you exist in the present (as both your physical/mental capability and your will to do something are determined by your material context at the time) and once something is in the past it cannot have been done any other way without changing the material conditions that shaped you back then, which you cannot do. Of course you can get better at doing the same sort of stuff by practicing it over and over, but you'll still always be doing "your best" each individual time. Even if you deliberately half-ass something you "could" have done better, your choice to half-ass it was calculated based on your conditions at the time, and so you'd never have chosen to not half-ass it unless the conditions were different (which again you cannot change).

Personally I dont worry about it too much.