Add the oil much more slowly next time, and it really helps if your bowl is cold I used to work at a restaurant where we did this in bigger batches and I used to do it while standing in the walk in fridge, but keeping your bowl in the fridge until you start will help alot. Also when making homemade mayo I can not emphasize whisking vigorously enough, like by the time you're done you should feel like you just worked out your arms.