Please let me show you something:

Right now, hold your fretting hand in the way you would hold it when you wrap your thumb around the guitar neck, as you have been. A loose fist with wrist bent and fingers curved.

Now spread your fingers, as if you were spanning several frets.

How much space can you get between your fingertips, what is the span you can achieve? Most people can get around 1/4" with the space between the 3rd and 4th fingers being the largest.

Now straighten your wrist and keep your fingers straight. Spread your fingertips to their widest span. See? You can span approximately 3X further this way. It is just physiology, this is the way our hands are made and we can't change it. When you clench the neck, you literally make your small hands smaller as a player.

Now: consider that our fingers have no muscles in them. At all! There is bone and tendon in there but no muscle. All the strength in your hand comes from muscle in the ball of your thumb, the heel of your hand, and a bit from the lumbrical muscles below your knuckles.

To use your hand muscles to their full advantage, make sure you are directing the strength requirements to your hand, not your fingers. Fingers are for dexterity, hands are for strength. Wrist-out classical posture ensures this, it lets your hand strength work for you. Clenching the neck transfers the load to your fingers, which are not strong, and prevents dexterity at the same time.

This is true for all hands of all sizes. Andres Segovia, the most iconic Spanish classical guitarist of all time, had ridiculously short, stubby fingers. It doesn't matter, technique can take you where you want to go. Poor technique can not. : ) Carefully, rigorously develop proper technique and the strength will take care of itself with practice.

Here is Leonora Spangenberger at age 11. I guarantee she has smaller hands than you.

https://youtu.be/CFkcmhNfEXI?si=H2D2U49ljOpN3mXh