After approaching each group of targets, just continue to drive around the block normally. There is no reason to damage your car trying to reverse or spin back around. The targets do not run far. Simply drive normally around the block until your partners can start shooting them again. With the last group of Balla's, drive your car down the path and through the tunnel to run them over. Turn around and repeat until they are all dead. Since this mission is not timed, you can drive carefully to a Pay N' Spray between drive-bys to get your car's health bar restored. You will eventually have to go to the Pay N' Spray anyway at the end of the mission to lower your wanted level. That visit will be complimentary, but any others will be charged.