How do you get out of Herbology class?

Are you in the garden you got the diffindo spell is that the cutting one if it is go back to the garden where the ghost dog things are if you look up you will see an upright bridge held up by ropes use the cutting spell on the ropes and the bridge will fall but be careful becaue you will get imps come down and try to attack you so you gotta throw them in the hole in the tree then you cross over the bridge and into the cave you come out of the cave but be warned theres a mountain troll there use the spongefy spell on the slab hes on and boing up to the tree abd crawl along the ledges and jump over the platforms if you do all that successfully you will end up back in the greenhouse confronted by a flower plant trying to eat you do nothing a cut scene will appear and proffessor sprout will appear and guide you away there for ending the level hope that helps