My (24/F) boss (40s/M) has asked if I can work on a day that I requested off for vacation. I've already bought plane tickets and made hotel reservations that conflict. How do I tell him I can't work?

I've had my current job since September. I love it - I would even say it's my dream job, and I feel very fortunate to have landed it at my age.

I moved to a new state for this position and have only seen my friends and family a handful of times since starting. About a month ago, I asked my boss if I can take off March 14 - 18 so that I can go home to Texas. He said sure, that would be fine, and that I should email him so he wouldn't forget.

I bought my plane ticket home for the 11th, and made hotel reservations for that week.

I get to work today and see an email for my boss. He's asking if I can work the 14th and then have the rest of the week off. He says someone else is asking for time off at the same time as me, and if I worked that day it would help.

I'm annoyed, because 1) I asked him for these days off several weeks ago, 2) I don't want to change my plans and possibly lose money, and 3) this is the first "vacation" I'll be having in a long time.

I don't know what to do. I LOVE this job and don't want to do anything to jeopardize my place here. I'm afraid that if I tell my boss "No, I can't do that," that it will make me look bad and somehow be bad for me in the long run.

I know this might sound dumb. I'm generally a people-pleaser and am also easily intimidated by people.

tl;dr: Boss wants me to work a day that I've requested off. I've already bought a plane ticket and made hotel reservations that conflict. I don't know how to tell him I can't work like he's asked me to.