You don't want to pinch the barrel or the filament may get stuck, as well as the flow rate out will also be lower.
If however you use PEEK instead of PTFE, you can try using a high temp threadlocker, eg LocTite 680 to secure it in.
Though to use a thread locker, you will have to use a plastic that resists some chemicals like PEEK and not PTFE, as its super non stickm so threadlocker would not stick to it.