vaginal cave???

so when i lay on my back and i put my finger inside myself it feels like its just one big gaping hole. never had a baby and never even been with a man only women. i looked online and found this old forum from a few years ago where a bunch of girls said they experienced the same but no one really had an answer to it. is this normal? wtf is wrong with me? why is my vagina so large? will this affect sex??? someone help