Do you still have the cup you bought your betta in? I just use the cup to scoop them up when they're at the top of the water. Mine freak out over the net but the cups don't bother them at all. They're already in before they know whats going on.
I would suggest putting the net into the tank, wait till he swims in it or gets close to it, net him quickly and swiftly and put him into his water change cup. Simple as that, you don't want to chase him with the net or that'll really freak him out.
When I am undertaking a 100% for the 1g hospital tank, there is a mug in the water as a cave. Usually the lil dude is used to it, and I just wait until he is near the surface and slowly push the mug into the water to cause a current into the mug. Usually he is taken in with the current, minimal stress or contact with him.
As previously mentioned, some will scoop the betta up, but my dude doesn't stay still when the cup gets near him. So that's not an option, and the net, well both my Betta's hate it now so that rarely works.
I use the cups they come in.. I put it near the top and when they come to investigate it, I dip it in. The suction from the water entering the cup is usually enough to get them. Sometimes it may take me two times, but normally it works great. One of my guys seemed to of always gotten a torn fin when I used a net to grab him, so had to make a change.
When it's time for them to return to their tank, I will tip the cup into the net gently and then put them in the tank.