I'd say that's fine. It really depends. Is this an event that's been held previously, can you ask co-worker what the standard is?
I've been to many black tie/formal events/weddings etc where invariably I am the most over-dressed person in the room (apart from the bride obvs!). Lots of people don't stick to the direction on the invite, lots of people's interpretation of what 'formal' is is different.
If you turned up to a formal do with nice heels, bag, hair did, and that dress I don't think I'd give you a second glance for not being dressed appropriately (and this from someone who has pretty high standards for dressing up for events)