That is a weaker
uvb bulb so you will definitely want it mounted in the tank. If you have the option though I think I'd probably ask if I could exchange it for a reptisun 10.0 or the reptisun 10.0 t5 ho.
If you get the t5 ho you can keep it on the screen, its much stronger, but you'd need to get a t5 fixture as most likely the fixture you bought is for the t8.
If you go with the regular reptisun 10.0 it is a t8 so will fit your current fixture. You will still want to mount under the screen though.
But if you cant exchange it no biggie. Most of us don't use that
uvb bulb here simply because the reptisun and Arcadia bulbs last longer and have a better output.
-Brandon