Amanda Bynes -- Denies Trampoline Trip, But Witnesses Say ... It Was Her!

Amanda Bynes is ADAMANT ... photos taken at a trampoline facility last night in Buffalo, NY are NOT her -- but multiple witnesses think the woman DEFINITELY was the alleged bong-chucker.

It's pretty bizarre ... pics surfaced of Amanda wearing a brown wig at the upstate Sky Zone ... and she went BANANAS on Twitter, cussing out bloggers who posted them.

"THAT'S NOT ME!" she tweeted, adding: "I've never been to SkyZone! That looks nothing like me!"

But TMZ spoke with several Sky Zone employees and patrons -- and they're 100% convinced it was her. What's more ... Amanda left a paper trail.

"Amanda had to sign a waiver," Sky Zone owner Rhonda See tells TMZ. "She has the same DOB and same tattoos ... she checked in using her middle name and same last name. She did not use 'Amanda.'"

Witnesses say Amanda was disheveled, frantic and distracted when she arrived around 7:15PM, asking guests to delete pictures and bumbling around during the tutorial.

"She wasn't really listening," fellow patron Christopher Zukas tells TMZ. "She kept leaving the group to go set stuff down and would come back. During the jumping she wasn't able to follow the rules and was even knocked over by a fitness instructor teaching a class."

Other witnesses say she calmed down after 20 minutes and happily bounced for about an hour -- seemed to be having fun -- then left in a waiting car.

Amanda got pretty detailed in her Twitter rant/denial ... going so far as to assert: "I don't own a brown wig!"

Just one little problem with that story ...