on full screen + great resolution !

hi … (bone and muscle app)
i have computer with 2560 x 1440 resolution
and my application is lauched at 1700 x 970 resolution
but my question is when i choose FULL SCREEN
the app fills all screen, but pixelated, i mean , the 3d break to much
please how can I do , to tell unity 2017 when go FULL SCREEN
take advantage of the maximum possible resolution.
TWO PICTURES BELOW

here a picture the normal resolution NO FULL SCREEN3281385--253826--borrame muscle 1.jpg

and a second picture (same)
but here on FULL SCREEN … !!!

.
3281385--253827--borrame muscle 2.jpg

any help will apreciate so much …
just to know how fix ON FULL SCREEN the same resolution or a 400% better resolution please.
thanks

any idea ?