This is what I mean… you will definitely have read issues. Try something like this…
You should not need to smash the proxmark into your hand. What I would do is feel your hand with your finger and find exactly where the NExT is, then mark your hand with a marker or something to clearly show where it is. Then you can pick up the proxmark gently by the USB cable and hold it such that the edge of the LF antenna loop rests directly overtop of it. You can confirm which end of the NExT has the T5577 using lf tune. Once you’re certain, you can run the command.
Don’t forget you can also use the delay command to make things much easier…