Call him. Ask if he will take a money order. If not, wait until race day and pay him cash. Im sure he would have taken cash instead of your mothers check. Most tracks do not take them especially a 3rd party check. Try not to make excuses for it not being paid yet. He probably dont wont to here about your personal problems for one. Ask him straight up how he wants to get the money. Most likely it will be in person and cash. Ask for a receipt if need be. Not trying to be wise, just pointing out the truth. If he still dont want your money then just show up and pay to race.