Double dosing = bad, however, the chances are you're not on the highest possible dose of of the drug anyway (i.e. the normal therapeutic dose is around 20mg, but you can go up to 80mg safely), so you're probably not doing yourself any major harm.
However, mood-wise it's likely not great for the therapeutic effect. You need to take antidepressants regularly and consistently for them to achieve the desired effect.
And just to clarify, taking a double dose won't make you happier. You can't take a whole box of antidepressants and feel ecstatic, it's simply not how they work, sadly. It's more likely you'll feel a whole lot worse because of the side effects of upping your dose.