The "se" in the verb "ducharse" is a reflexive pronoun, indicating that the person receiving the action is the same as the person doing the action. Reflexive verbs like this will use one of the reflexive pronouns "me", "te", "se", or "nos". You'll most often see these reflexive pronouns before the verb, but in a phrase like this with multiple verbs in a row, they can be affixed to the end of the reflexive verb.
- Yo me peino cada mañana. I comb my hair every morning.
- ¿Te duchas hoy? Are you taking a shower today?
- Disculpe señor, ¿como se llama? Excuse me sir, what's your name? (How do you call yourself?)
Using "need" instead of "have to" is probably okay; I've noticed Duo can be a little inconsistent about whether it accepts those interchangably or not so you could try reporting "you don't need to shower now" if it isn't accepted.
The real issue with your sentence though is that you made it a question, whereas the sentence you were asked to translate is a statement.