Turn to the left (above where you entered the room) and place a portal up here (so it’s opposite the one still near the gel). Bounce up to the portal, step through and set the cube down on the square panel.
Now look up high and there’s now a new light-coloured wall panel that will have rotated into view. You need to place the exit portal up here and bounce back across to the entrance portal now opposite you.
You’ll want to jump through this portal and use the velocity gained to bounce up to the high ledge directly opposite you. Step through the force field and you’ll spot two walls coated in the blue gel.
Once you enter the room, divert your attention to the tiled wall panel on the lower ceiling in the right-hand corner (where the moving platforms moves under). Set your exit portal here and then fire your entrance portal at the tiled wall at the end of the Repulsion Gel.