New aftermarket Metra Antenna coax is 10ft, can i shorten for tiny car?

after running and lining up the antenna coax with it's finaly resting spot, it's 3+ feet too long, the fem end pops apart REAL easy and looks no harder to terminate than a TV coax other than soldering the one tiny piece. also looks like the factory did a shite job with the shield/drain wire.

anyways do car stereos need a specific ohm like CB or HAM or would whacking off a few feet make a difference or maybe even improve things?

didn't wanna bunch it up, kink and mash it in only to have it shredded by the sun roof or something.