How to make doomsday style ctf but dosent end the game after 3 cap

I haven't played with the Doomsday's game mode in Hammer yet, so I'm not sure if it will help, but I think you could make an actual CTF, edit its properties to the ones you want, spawn a prop_static or prop_dynamic prop using the Rocket's model, and place the capturing's colume there.

The amount of flag caps is dependent on the server's settings, not the map. You'll need to set the server command 'tf_flag_caps_per_round' to 0. (This means that if you want your map to be imped, you'll need to have a staff member on-hand to set that command manually)

As for disabling the CTF hud, you can add a tf_logic_hybrid_ctf_cp entity to remove the capture counters and just have the flag compass, or use the tf_gamerules entity to force the map to use another HUD entirely (capture points or payload).