ANSWER - Fire, as most witches will tell you, does have a bit of a mind of its own. Burning your curtains is practically a rite of practise for a witch and if you haven't achieved at least a few accidental explosions then trust me - you will! You're choosing to read quite a negative significance into the candle flame but I would say that getting a response like that actually sounds quite positive to me. I'd certainly consider the possibility that a fire element was responding to the work you are doing. Equally I would also consider the fact that fire does sometimes just do its own thing. Not everything always has a significance and we'd all go mad with confusion if it did. There is no reason to assume your spell has not worked and no reason to assume it will go wrong. Generally with spell work, it works or it doesn't, there are few circumstances when a spell rebounds with negative repercussions on the caster.
One other element of your question interested me, you refer to what you are "asking" for. Magic doesn't really work like that, you are the conduit of the power, you are not asking for something to happen, you are consciously taking steps to make it happen. Try and approach the work you do more in this spirit and I think it will give you more confidence that you are in command of the situation and the spell isn't going to rebound and harm you.