@Litorrally Diving
Been there done that. I was a disaster on my first couple of dives.
So point 1. Go weight check yourself, you know the drill you've been taught it and can do it (with a full cylinder I like to sink until my head is just below the surface, then exhale to prove you can descent - remember you only need to go down a couple of feet before the weight of the water above you take hold
Point 2. The body has a natural reflex, it's called "The Fight or Flight" reflex. You'll no doubt have experience the second stage of it before, when you've had a scare and the adrenalin has kicked in?
For the first part, your diaphragm drops to increase your lung volume, allowing you extra oxygen to run. For us divers this means a sudden change in buoyancy. It happens a lot with new divers because their brain hasn't relaxed to the underwater environment. It doesn't need much to trigger it.
You'll have been told (probably) that when you get more experienced and relax more you'll reduce the amount of lead you need. This is why.
Point 3. You were shallow. Pressure changes are quite large for small changes of depth so everything happens fast.
Final point, take time in your gear to run your hands around in - both on you buddy check and in the water. It does take a little time to be able to instinctively put your hand on the right place, so don't beat yourself up. Rome wasn't built in a day
You've had a learning experience, we all have them. You'll have a few more as you get more experience. A sign of a good diver is that they recognise it and try to address the issues as you have done.
Keep smiling and keep having fun