How will i properly use listerine mouthwash?

Hi everyone! I've been trying to start using mouthwashes and i chose listerine. It says on the directions that i should use it undiluted it meas without mixing it with water but when I gargled 20ml of it undiluted my mouth felt like it was burning. Should it really be diluted or undiluted? or should it mix it with water or gargle it as is?^^ thank you in advance