There's no way to give you a percentage. We can tell you that the possibility of pregnancy is there. There's no such thing as safe sex, only safer sex. No form of birth control is 100%, the condom doesn't have to break in order to fail, and there's plenty of sperm in pre to get you pregnant.
Wait another week. If you haven't gotten your period, try a pregnancy test using first morning urine. If that test is negative, wait until your next period is due. If you miss it, test again or see your doctor for a blood test.
The only way to avoid pregnancy 100%, is to not have sex. There are women on this site that used 3 forms of birth control, all correctly, and still got pregnant. Any time you have sex, you could get pregnant, with or without protection, and frankly, condoms are the least reliable form of birth control.
Good luck.
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