Yamaha Acoustic Guitar: Are My Hands Too Small For A Regular Guitar?

I’ve been trained in playing classical piano and can handle most pieces well except ones written for larger hands. I don’t consider my hands to be really small, but I am petite of build and my hands are slightly smaller than normal. I taught myself guitar many years ago, I’m 32 now, but always my problem with guitars is that I can never seem to do the chords like B maj for example, properly (i.e. any chords that require pressing a finger on all the strings at one go). I’ve tried and tried and its just not working. I have a Yamaha acoustic guitar with steel strings. Is it because I should go for a 3/4 size guitar? Or is there some way I can train my fingers to be able to play those chords? And I was under the impression 3/4 size guitars are for children… will it be odd if I use one, lol ?? :)
Don’t think I am “grabbing” the neck all along. Its not that my index finger can’t reach all of the strings and press down on them, its just that when my finger presses down on them it never seems to press down hard enough and the sound of the strings become muffled sounding or muted as a result.
b major chord is the absolute worst. f minor etc. are all manageable and unless my fingers are already tired, they are okay to play, but the placement of b major chord fingering is my absolute bane having to squeeze all 3 of my fingers (3rd 4th and 5th) into the same fret. i suppose its all down to practise. maybe i should try nylon strings.
I just measured the size of my handspan. Its just under 8 inches. Is that fine for an average sized guitar?