Try and remember a monologue that doesn't have difficult words for you. One that has the appropriate language for your age. With simpler words that you are most comfortable with. Just keep repeating it. But say it like you are already doing the play not like you are desperate to remember. Hope this helps.
When I had to memorize them I would break it into parts repeat the first part how many times as needed then moved on to the second part , do the same process but after I repeat the second part I would recite the whole first half and see what i got wrong . That's my pattern.