Okay, I need some help with embling a Halloween Costume?

Hi, my cousin's church is having a little Halloween event that I go to every year and last year I dressed up in a long black scream costume without the mask, instead, I used a witch mask and it turned out good. No would could really recognize me. Well, this year, I am taller and bigger of course and the robe got split down the middle. I can still wear it but the front is open and my clothing shows, but U don't know that it's such a big deal, but is there any way I can fix this without sewing it up or buying another costume. To tell the truth, if I sewed it up, it would probably rip open again. The robe looks pretty good as a cloak but what can I wear under to where I won't be as visible. I'm a bot by the way but I never take off my mask in front of so many pple so not many people will know I'm a boy. Bottom line, how can I fix up this robe without sewing it or buying another one in a way to wear my under-clothing wont be such a big deal? Thanks to all who answer!!! :)!!!!