Potty training DS was hell on earth. He's 6 now and still doesn't always make it to the loo on time. He has to be almost strong-armed into the bathroom in the mornings before he leaves for school. I was bracing myself to potty train DD (who is 2.5 years) but lo! she got it almost instantly.
We started on Monday, there was one wee accident that day, a combined wee and poo accident on Tuesday and a poo accident today. Otherwise it's been plain sailing. On Friday I was in the loo when she appeared asking for the potty. I asked her to hold on and finished up quickly but by the time I got into the other bathroom she had put the toddler seat onto the loo, climbed up and done a wee all by herself.
So if you're having trouble/had trouble last time, take heart. It's probably just one of those things, you're not doing it wrong and next time it might be a piece of piss (pun intended).