Windows and doors open is way louder than sealed 99% of the times. Its the same principles as ported vs sealed. If they meter on the dash or kick on the passenger side, you want your driver door opened or driver window cracked halfway down or fully down while the passenger side is fully closed up.
If your box is not above the window line or past the B pillar, you should have been novice 0-1500 not 1500-3000. You would have at least taken home a trophy.
Sound deaden will either gain db at a lower frequency but not necessary getting overall louder, some of the times after deadening some people lose dbs on the meter because their car was louder when it peaked at a higher frequency. What you can do is 1/2 plywood your roof with heavy duty PL adhesive and brace any part of your car from flexing(make sure you make it look stock or else you'll get your @ss called out on it and get disqualified). Deadener deadens sound and lowers resonance aka lows cabin peak frequency. It'll sound better on music but gaining on the meter is a luck of the draw. A member on here lost dbs deadening his grand caravan thats why i mentioned this.
Dont swap gear, stick in your class, stick with the same gear, read up on rules
http://www.usaciworldwide.org/Rules/2018USACIRules.pdf. Learn every trick possible to gain dbs. Play around with box and port tuning mods. Play with the seat positions, sun visors, how clean your car is, the weather... EVERYTHING affects your db scores. You need to know whats your ideal metering conditions and setup along with knowing your best frequency. Definitely get a meter.