Learn to keep stroking
Okay stop stroking before you have an accident. Massage your swollen balls, while you listen.
You should have noticed that it is really hard to find the right speed to keep yourself on the edge, without backing off. You know why? Because it's not a constant speed, it'll change depending on your arousal. Many facts play a role, for how long you have been denied, and for how long you have been stroking, and most of all for how long you have been riding the edge.
That means when you keep riding the edge, you have to continuesly go slower to not go over it. You have to slow down, and you have to learn how fast to slow down. Each boy is a little bit different.
As you go slower and slower it will almost look like you have stopped stroking. Again thats a bad thing. So you have to learn to hold back better, to keep up a faster edging speed.
How? Well by training to ride the edge many times ...
Start stroking again, and go faster, then ...