It is good to check context and other translations.
v2 says "let me not be put to shame, let not my enemies exult over me" (RSV)
These are two ways of saying the same thing. If I am overcome by my enemies, I am "put to shame".
So v2 is a personal request for help, a wish for the future.
Then if we look over v3 we find a more generalised version of the same plea;
"Let none that wait for thee be put to shame"; that expands the range from "me" to "everyone who trusts in you". Let none of them be overcome.
Then "let them be ashamed who are wantonly treacherous" is the generalised version of the second half of the plea. It expands the range from "my enemies" to "everyone who acts as an enemy". They all need to be the defeated ones.
The only thing that you need to do is to be one of those who can say "O my God , in thee I trust" (v2).