Im scared of my friend getting me horny

Sorry if i i misspell something, english is not my first language.

(19m) I've been informed 2 weeks ago that me, my family and my friends (19f) family are going on summer vacation together and she will share room with me.

I know her for years (and had crush on her long ago) so im fine with that but you know how it is on vacations: hot temperatures, water, bikinis, alkohol etc.

Also she is really pretty girl and now im scared that she will see my boner or idk

Of course I've fantasized of horny things that can happening between us and little bit of me want to this things happend but don't know how to trigger such situations.

On the other hand i think she is not attracted to me and I don't want to ruin our friendship

What should I do?

Do you have andy tips how to not get horny?

Or in the contrary trigger sexy situations and mood?