you are thinking in a bit of a confused way [I think... LoL]
You seem to be thinking that you can copy and paste some abstract something... but it do not work that way..
What you copy and paste is a 'something'... in reaper it is what we call an 'item'... i.e. the orange thing you show is an 'item'...
Your only problem is that the item is not exactly the length you want it to be.
What we are trying to explain is how you first fix that item, no matter if it is audio or midi, so that it is the exact length you desire. After doing that copy and paste is easy and will do what you want.
There are a few ways to make the item the length you want...
Let's try another one:
make a time selection from the end of the orange item to the start of the next measure.. [you may need to turn snap off first]
open actions list and in the filter type 'empty item insert' without the quote marks...
You'll find the action, run it...
You will get a small empty item the size of your time selection
OK, now select the orange item AND the empty item and hit Glue...
You will get the orange item with the empty item added to the end of it so that now the orange item is the length you want it to be...
so then do whatever with it... copy paste or drag it out as a loop...
from what I see in your picture, you don't need to copy and paste... once the size if fixed you can just drag it out as a loop for as much as you want.
NOTE:
OK you could do a variation on this like so:
leave snap ON, make the time selection from the start of the orange item to the start of the next full measure...
Now use the Insert empty item action.
Select what you get and the orange item and hit Glue.
NOTE TWO:
Reaper has its own vocabulary... things are called names which might not be how they are named in other DAW's...
It really helps to learn the reaper names so we are all speaking the same language... ...makes asking questions and getting help mo'betta.