Well if it's tomorrow then I guess you have three options
Play your familiar London setup, just know you need a win and maybe take some more risks than usual
Play a d4 opening that is considered good at master level too, such as the Queens Gambit- it's a serious try for a win
Play something offbeat and aggressive that your opponent won't know, such as: 1. d4 Nf6 2. g4?!
I don't think the 3rd option is very good, well atleast the 2nd part, playing something offbeat is fine, but don't play something that is just bad
It's just an example
@Water_Flame Maybe play the first few moves like London and depending on what he does I play either c3 or c4. See the example game I posted on the last page
Hey folks do you think I should play an aggressive London System or play d4 c4 into the Bogo-Indian Defense
Or I could play a few London moves like d4, Bf4, e3, Nf3, and at the right time play c4. If he trades dark squared bishops with Bd6 and Bxg3, I can play c4 and get a more favorable QGD position.
IM eric rosen made a study about the london system with collected games and some annotations
lichess.org/study/FErc0llBprobably a good idea to go through them and get some sharp ideas in the london system.
Surprise the crap out of him with a King's Gambit!
I'm just joking, just play to your strengths not your opponent's weaknesses.
Do not overthink it. Choice of opening is not important. Try to play good moves and not blunder. It is wrong that in a must win situation you should play aggressively. There are famous examples where top players in must win situations were successful with quiet openings.
One last thing- I have 1.5 hours left to prepare- What if by chance he plays this line:
Should I play e4 there? It looks better than the other options but still I hope the position doesn't simplify into a draw.