It's normal for bokashi bins to smell slightly acidic. If it smells bad then your scraps are probably rotting instead of fermenting.
Bury your rotting waste in at least 10cm of soil in the ground or a large pot of soil, wash the bin thoroughly, and start again!
To keep this from happening in the future, make sure you:
Close the lid tightly
Add enough enzyme spray
Tap out bokashi juice frequently
Keep the bin in a relatively cool area