Whether flying wings level or in various degrees of bank you need to be able to maintain an altitude.
When you advance into instrument flying you will be expected to fly at set altitudes whether flying straight and level or in a bank.
The fact that you have descended means that the input for various degrees of bank and the required pitch and power to maintain Altitude and speed are not correct.
I would not be afraid of "putting the aircraft back" to where it should be!! as only then will you get the true feel of what is required.
I have flown with experienced pilots who descend through an assigned altitude and almost sit there frozen until the controller picks up on the fact that they are 200 feet too low!
There are times for finger tip control of attitude and power and times when you need to grab the bull by the horns and have the confidence to place the aircraft where you want it smartly.
it is about confidence and feel so if your not where you should be put it back
As John above said its a matter of pride in your flying to aim for perfection to be able to fly varying degrees of bank and to be so precise that the altitude needle does not move and you roll out on the nail.
To accept a lower altitude as your new altitude is just sloppy flying and that is not what we all aim for or aspire to achieve.