If you want to do English, then I see no point in doing Western!
I'd switch back to English. Just remember, it's not a race. No one will force you to do things that you are not ready for - have a word with your trainer and say that you are a little nervous. Don't feel stupid, I've been in this kind of situation, I talked to my instructor and now I'm a lot happier than I was! You're doing riding for pleasure so there's no hurry to suddenly start jumping 4ft poles, like the others have said, work on your flatwork, get cantering comfortably and in no time you'll be jumping!