Unless you are a totally new, inexperienced driver, it's no big deal. If you have ONLY driven automatics, you have a bit more to learn, but so what? It's a skill that stays with you forever.
Take a few driving lessons; the objective is to teach you how to pass the test, not how to drive. Your auto insurance premium will typically drop after you get a full UK license, and yes, this is also a useful ID.
Did you stress so much in the US when you got your learners permit? And then you license? Probably not - adopt the same attitude, and you'll be fine.
DH's older grandson (English born and bred) failed the written test on the first try, but he was far too 'smart' to bother reading the book. The younger one passed written and practical first time.