Help please

I'm new to sequencing, and I am having major issues with my sequences. I have purified my PCR product using a standard PCR purification kit, and had it sequenced. The first part of the sequence was what I expected and where it should end, it doesn't. Instead it carries on and I have no idea why it carries on. I had run the PCR product on an agarose gel and there was only one amplicon. The PCR product size is pretty small (~90 base pairs) and I don't know if it's because of the product size or something wrong with my primers. Any help and advice would be greatly appreciated.