What am I doing wrong when shaving my underarms?

Ok so I have tried twice now and every time at the top I am left with a lot of stubble and on the bottom there is still hair that won't come off. I have tried shaving in pretty much every direction but nothing seems to be working. I haven't tried up cause my mom was all like, oh no don't shave up you'll snag all the hairs. And I shave mostly down but I've also tried diagonal up cause it seems to be growing out and down. I'm not sure what to do and I'm leaving for vacation on Saturday. I use shower gel and I do it in the shower so it is wet.What can I do that I haven't already tried?