does your body save leftover vitamin d?

Yes the body can reserve vitamin D for later use. In fact the number one place that the excess vitamin D is stored, is in the liver, along with many of the other essential micronutrients. However if over time not enough is taken in via either exposure to the sun, via diet (such as fish, seafood, and shellfish), or through oral supplementation, to meet and keep up with what's used, you will over time reach subclinical lows or even  if longer is gone become outright deficient. However as for vitamin D2, the human body doesn't actually store that, instead it will undergo a conversion process to what the body needs. Also the conversion rate for vitamin D2 is not that good, with it in a healthy individual coming in, with an at best of twenty to one ratio.

Vitamin D can be stored in the body for a long time. (link 1) Vitamin D-2 and D-3 can both be stored in the body for approx 2 months (link 2). When the stored D is released back into the bloodstream, it can circulate in the body for about 3 wks.

no ones body does that

No. ....body doesn't STORE vit D ... also supposed to take vitamin A with it .