I don't get too stressed about these endings. I can't be expected to go through a mental matrix to see if I've got the right ending for an adjective mid-conversation. I figure I'm doing well if I can recall the gender of a noun at all! They will come with use and listening. But if you end an adjective with an -e instead of an -es, so what? Most Germans are happy that you even try - and they don't always get it right either.