The correct way to release the slide is to either pull the slide back or use the slide release. Either way is fine.

How are you using the slide release? I use my left thumb. When I insert a mag, my left thumb is in a good position to hit the slide release. I only use my right thumb if closing the slide one-handed. May require a bit of a grip shift to get enough leverage. Of course, this is assuming you're right-handed.

It may just need some breaking in. Give it some time. Use it normally. Or you can pull the slide back to release it. Try both methods. You may prefer one over the other.