wont let me renew contract

You will have to renew it when there is 1 race left on the contract. For example if you have 10 races left on a contract and you extend by 10 races, then when the first 10 races are up the option to extend becomes available again.

In your case because you renewed for 1 race the option to renew will be available again when this 1 race is remaining.

Unfortunately not, you can only have one active extension on a contract at a time.