In world 5-1 shy guy jungle I can't find the 3rd scrap of bridge to get..

You're probably looking for the one near the garbage, right? Just get a Vacuum sticker and use it in the area where all the garbage is. The Shy Guy with the bridge scrap should be revealed after this.

From the main area, take the right exit and drop down to the lower level where the red flower is planted. Walk behind the red flower and to your right to find a small cave with a HP-UP Heart inside. To the left of the red flower is a bush that can be squashed with your hammer, revealing tape that can be peeled and made into a little step. Whack the red flower and use this step to quickly cross over the flower before it becomes active again. In the next area, head over to the next red flower and find the small blue flower to the left of it. Whack your hammer against the wall to reveal a hidden block that serves as a step when you are trying to cross the red flower. Head into the tall grass and scare the Shy Guy with Bridge Piece into the direction of the ramp leading to the higher elevated area. Push him towards the red flower and he will jump in, leaving the crumpled Bridge Piece on the other side. There is also a Secret Door with Tailor Shears inside. Head back to the main room.

Back in the main room, walk around in the tall grass and push the Shy Guy with the Bridge Piece into the upper left corner of the area where the tall grass doesn’t grow. Defeat him and grab the last Bridge Piece. Head over to the purple void and place the three Bridge Pieces in their correct spots to gain access to the piece of the Sticker Comet.