You pretty much summed it up when you stated that you were underpowered on your main and over powered on your jib! Lee helm is caused when there is greater force pushing the bow down then there is force pushing the bow up.
If you think of it as a balancing act, and the mast/keel as your balance point, when you have Weather Helm, your main is forcing your bow up into the wind, you would then try to de-power the main, flattening reef, drop the traveler to leward, etc. When you have a balanced set of forces, you will have little or no weather helm.
When you have Lee Helm, your jib is overpowering your balance, and the main is not generating enough force to counter it. You need to then power up the main, get the sail fuller, move traveler to weather, etc.
In your case you were probably not interested in powering ANYTHING up due to conditions, and maybe should have thought about dousing the jib and sailing under main alone. You would get a good deal of Weather Helm, but that is preferable to Lee Helm in almost any conditions.
You may also want to look at your rig tune. As the wind built, you may have had excessive headstay sag or your mast may have begun to fall off more than is desireable to leward, also causes of Lee Helm, as the shift of your center of effort moves to leward.