LED's are obviously a type of diode. Diodes usually have a fixed voltage drop across them (required in order to bias the components to conduct) regardless of current. So it is possible that your voltage is not high enough.
Although to be honest, your numbers sound like you have enough. In any case, usually people put their LED's in parallel. Its easier to control the current going to them this way (by sharing a single resistor) and to make calculations.