Two mistakes....first you cut them back...which encouraged the plant to begin growing. There was sufficient energy in the plant to begin the process. It is showing the results and because of low light, it is also showing up in the color of the leaves.

Ask yourself....why should you water a plant, then place it into darkness. what is the water supposed to do for the plant in that environment? Also, you gave it soil...to feed on...especially fresh potting soil which has fertilizer in it. So, in effect, you pushed it to grow.

Besides, possibly where you have the plant is warmish....higher than it need be and the temperature, along with the water you have given the plant, is enough to cause it to grow. Mind you, it wont grow much...it cant...it doesn't have the light and the temperatures to do much.

To slow down a flower, we bring the plant back from the light and give it cooler temperatures. If you were to do the same thing for your geranium, it will also slow down.

The plant need not have been cut back at the time you did.
That can be done when we wish to bring the plant back...and that will be in another two months....mid February to mid March when the sun values return. Next Wednesday is the start of the winter solstace...the shortest day of the year...and from then on, the sun begins its long voyage back.

Take the plant to a place where you can unpot it...rid it of all soil around the roots....now it cant be fed....
remove any weak or damaged leaves...or leave them be...as you choose....leave the rest of the plant as it is ...and take it to a much cooler area of your basement...and hang it up....or place it in a kraft bag and let it dry out....completely. No more watering. No light, no water, no raising of temperature....no nothing.
In mid February, we bring it out, cut it back...yours probably wont need much of that....but examine the roots anway...and re-pot with fresh potting soil (do give the pot some thing to raise the soil away from the drainage holes)
mix if you like with the sand and vermiculite to improve the drainage capability.....take it to the best window you have...(north will not do)....east, south or west exposure.
Water it well, water it until drainage is seen in the saucer below...allow full drainage, then dump the excess.
Don't water again until new leaves form...then begin to fertilize 1/4 rate every 3rd or 4th watering.

The plant will produce a whole new set of leaves....and as the leaves mature out, you can increase the fertilizer....
the plant will also begint o bud up...depending on the amount of light it is given...so don't be too alarmed if the plant does not bloom until it is put back outside.
It will eventually produce a bumper crop of bloom.

Have a nice, safe Christmas and
a plant full of New Year.