I had it at a salon with a nurse once and a doctor at a clinic every other time. No problems but the difference in knowledge and competency of a nurse in a salon and a doctor in clinic was night and day.
A doctor explained the dropping thing to me, it can be fixed, it usually is due to the person doing a poor job. They should have booked you in for a review to make sure you are happy with the results.
Honestly, if you can afford it, I would go to a doctor at a clinic to have it fixed. Otherwise yes go back and if there is a supervising doctor there maybe ask for them to do it.
It can and should definitely be corrected, don't worry! It is corrected using more botox, but it's not the whole thing again, it's a couple of specific places, I think near the eyebrows.
Love botox, I have no shame in telling people I have it done. Usually I volunteer the information every time someone says I look young, maybe defeats the purpose, but it's true and people are curious for themselves!
How often does everyone have it redone?