One eye bigger than the other from botox? (Photo)

Thanks for sharing your question and photo. It is hard to give you an accurate answer without seeing a pretreatment photo. That being said, Botox injection into the forehead could result in eyebrow flattening or eyebrow ptosis (droopiness). I would followup with your injector to review your photos and to see if anything can be done to address your concerns. If this is related to the Botox, then it will resolve completely once the Botox has worn off. 

Botox effects are reversible. It is important to consult with your injector to evaluate if this is a side effect from Botox and they can go over the different options to achieve relative symmetry between the two sides. 

There is a possibility that the difference in your eye size is due to Botox.  Occasionally Botox can prevent the eye brow from rising the same as the other side.  This can lead to the heavy and full feeling in the left side.  It will return to normal within three months of the injection.  Make sure you inform your injector, so that they can take precautions on your next visit.