Is there a term for polishing something too early?

Well I normally hear - "You are doing that bass-ackwards!"

Which is just a nice way to say ass backwards, or doing something in the wrong order.

Ass backwards. The state doing (or having done) something the wrong way.

A nicer way to say it, "You are jumping the gun there."

To start something prematurely.

to do something before it should be done

I think that a saying that may fit your description is:

to put the cart before the horse

Fig. to have things in the wrong order; to have things confused and mixed up. (Also with have.) You're eating your dessert first! You've put the cart before the horse. John has the cart before the horse in most of his projects.

Here's a couple of IT specific terms.

In the context of IT premature optimisation is a common term, with the phrase 'premature optimisation is the root of all evil' coined.

While this explicitly refers to program optimisation, it can also make sense in other IT contexts. For example, if you're talking the ideal arrangement of buttons when mocking up a quick working prototype, saying

I think we're suffering from a case of premature optimisation here

would be perfectly understandable and get your point across.

Additionally in IT, there's the You ain't going to need it (YAGNI) principle, which states "Always implement things when you actually need them, never when you just foresee that you need them.".

You might say

This is breaking the you ain't gonna need it principle.