When I was younger I found I was absolutely hopeless at any sport such as cricket or tennis, and considered I was a bit of a failure as a result. After all the other students could go on the cricket field or tennis court and hit the ball where the wanted, looked easy until it came to my turn.
I never had my eyes tested until I was around 15 when I had difficulties reading the blackboard, then looking down at my work on my desk.
It turned out I had an eyesight problem, which fortunately could be corrected by glasses.
The reason I was no good at those sports was because I literally could not see the fast moving ball, and did not realise I had an eye defect, I just thought everyone else was cleverer.
You too have an eye problem, one that may well stop changing when you are a little older, and there are remedies for it, temporary now, maybe permanent later. It is small wonder you have fallen into the same trap as I did and assumed everyone else was more able, putting yourself down.
If they can see better it makes a world of difference. It is no reflection on you or your basic abilities, just that your sight is holding you back. I'm sure by now you will have visited an eye specialist and told the future gets better as things stabilize. That getting better does not just apply to eyesight, but all your abilities as a result.
So please hang in there, try to realise you are fine, not stupid at all, and you will end up just as able as others and in the meantime are doing well just to be able to keep on going.