My stitches won't all fit on the needle - what can I do?

Sounds like you might need longer needles!

If you're using straight (single-pointed) needles you can buy needles up to 40cm in length from the site, but your best bet would be to switch to long circulars (cords around 80-120 cm long) which you can use just like straights. 

If you have interchangeable circulars then all you need do is change the length of the cable for easy length amendments. Within a brand (eg, Addi, KnitPro) you can usually swap any cable with any type of needle tip, but different brands are not compatible with each other.