Would it change the meaning of a sentence if I say "with" instead of "in" here?

Just curious, when are words hyphenated? Does the word "pain-cancelling" already exist?

Oftentimes, two words are hyphenated to create an adjective, so while the words may not be adjectives themselves, with the hyphen, they function as an adjective for the noun. This is called a "compound adjective!" So here, the words "pain" and "canceling" are hyphenated because they function as the adjective before and for the word "affect." The words exist separately, but they're used as one adjective in this sentence. Ex: She was the CEO of a well-established business. Ex: This is an old-fashioned dress. Ex: I made the gut-wrenching decision to move cities. => "gut-wrenching" means unpleasant or upsetting

What's "get off" mean?

Here, "get off" means to leave work at a scheduled or unscheduled time. "Get off" can also mean to escape or avoid punishment, to be excited, or sexually aroused by something. So one must just be careful of what context you use this phrase. Ex: She got off work early to fetch her friend from the airport. Ex: The student got off with a warning. => avoid punishment Ex: He get off on the adrenaline. => excited. Ex: People get off in bathroom stalls at parties. => sexual meaning

Does whopper mean what it means bcz it's similar to how people sound like when they see something big or unbelievable?

Not quite! Although I appreciate the creativity of the thought. "Whopper" actually comes from the word "whop," which means to hit something hard, or to set something heavy down. A "whopper" is usually something large, so perhaps it could be "whopped" or plumped down. Ex: Whop the bag onto the floor right there. => put something heavy on the floor. Ex: That book is a whopper. => It's a big book

What's "build up" mean and when's it used?

"Build up" is a phrasal verb that means for something to accumulate or assemble, or to become more intense. It can also be used for fitness when referring to making one's body stronger. It can be used in relation to emotions like excitement, and anticipation, or when collecting or gathering materials. Ex: I've been building up my collection of vintage toy cars so that I can sell them at an auction. Ex: My anxiety built up so much, but when I went on stage, it wasn't as bad as I thought it'd be. Ex: There's a build-up of pressure in the pipes, so they could burst.

What's he mean by "seven" here?

There're a couple of possibilities for "seven" here since the context isn't super clear! In relation to the previous line mentioning "heaven," it could be a reference to the party game "seven minutes in heaven," which is a kissing game played at many teenage parties in the west. Or, it could mean time spent together, either "seven days" of the road trip or that they have or will be together for seven years. Ex: I used to play "seven minutes in heaven" at parties with my friends and classmates. Ex: Oh, Jonathan and I have been together for seven years now. Ex: We'll be together on the road trip for seven days.