So google them

And yet you couldn't find a better adjective for "big"

Don't feel bad, OP. That's actually quite common. I remember one time, when I think I was still in middle school, I pronounced the word "epitome" (pronounced "eh-pi-to-me," for those who don't know) as "eh-pi-tohm" - but I used it with the right meaning. Luckily, the teacher who heard me wasn't a douche about it; he actually said he could tell I was a reader because I used the word right but pronounced it wrong. I would recommend looking up a word on the internet if you don't know how to pronounce it.

It's okay, OP. I was in honors classes all through my schooling and know many "big" words but hardly ever use them (though I find it is because my coworkers don't use "big" words and I dont by office culture assimilation). I commend you on your efforts! I definitely suggest, as others have, getting a dictionary app and listening to the audio. Plus some words are tomayto-tomahto so I wouldn't stress too much!

Reminds me of the first time I said guillotine. Apparently is Gee-a-tine not Gillo-tine. That was embarrassing.

I can relate to this. I read the dictionary as a child and so sometimes in a conversation I'll think of a word but then I second guess myself if I'm using it in the right context.

Mac computers have a speech option which has helped me when I am reading at times or look it up in the dictionary it will have a key for pronouncing words

Happens to me all the time

You were obviously failed by the system like the rest of us...

I actually really love when people do this (pronounce large words wrong with obvious correct knowledge of their meaning.) You can tell they read a lot which I find to be a cute and admirable trait.