my roots have turned ginger help?

I have light brown hair naturally but have it coloured blonde by the hairdresser. when my roots started to come in I thought I would save some money and use a home colour kit (used nice and easy). I only put it on my roots, left it on for 45 mins ( the box said 30 - 45 mins) but when I rinsed my roots were ginger. did I leave it on to long or not long enough?