Can't install TWRP on Galaxy A3 (2017)
For those that came here, the problem is that when booting, twrp is erased by stock recovery. The goal is to avoid the normal boot.
Firstly, uncheck "Auto Reboot" in Odin.
Then finish others Odin steps, and when you see PASS here we go:


Volume down+Home+Power to exit installation/start reboot process.
Instantly when something change (screen should turn black) switch to Volume UP+Home+Power (combinason to enter recovery mode), and there it should be okay.
(if you are too slow it will again boot normaly and twrp will be gone again).