This is what i did:
1: hide chat > minimize it to move it out of the frame
2: deactivate enter key with the program "killkeys"
This is how i used killkeys after download:
While "killkeys" is open, search for its logo in the right-bottom corner of the desktop.
Right click it
Options > open configuration (duno the real translation in english, mine is in spanish)
You can see a new window that contains text.
Search for this part "Keys_Fullscreen=". It has something written after the "=", these are some keys that are already bloked, u can keep them or u can delete them, in any case just write "0D" after the "=" or after the others. The "0D" is the code of the "enter" key. This how it should look: "Keys_Fullscreen=0D"
Remember to have the "killkeys" logo in the right botom corner in the active mode. (it has active and inactive mode)
Now it is already configurated and u can try it. The "enter" key wont be active during the full screen mode (i think it afects any type of full screen, inside or outside LoL).