Tom – the Shutdown and trap area are important and tricky. Alot of damage can occur to cars if the shutdown does not slow the cars and if the trap allows cars to fall on the floor.
If you are running glue the combination of the glue (heavier than the light glue used on the running surface) and shorted-rails provide braking. If you are Not using glue you may need to consider embedding block magnets (available from HaborFreight for 99c a pair) into routed holes in the wood next to the rails. These slow the cars by attracting the motor can and any steel in the chassis. Based on my experience you will need several pairs of magnets 5 to 10 pairs per lane spaced about 3-inches apart from the previous pair. #97505, #98406
https://www.harborfreight.com/pack-of-2-ceramic-block-magnets-97504.html
Since you ran out of room for a “bag/net” you may need to experiment with a ‘box’ made out of foam, such as used for pool floats (small life jackets and boxing practice helmets). The purpose of the box is to prevent cars from bouncing out onto the floor.
https://www.academy.com/shop/pdp/trc-recreation-texas-tech-university-sunsation%C2%AE-pool-float#repChildCatid=3812642
https://www.academy.com/shop/pdp/trc-recreation-kids-texas-a-m-university-super-soft%E2%84%A2-life-vest#repChildCatid=3812624
"... get on your bad motor scooter and ride!"
Sammy with Montrose