They both mean the same thing, the second one is slang and I would avoid using it unless you are talking to people who use a similar type of urban slang. To some people it will sound like you are cool and to others they will classify you as lower class if you use the slang version. The first one is good for all occassions. If you want to make the first one perfect, don't use "actually" because you already said "to tell you the truth," and both those phrases are conveying the same thing.

Yes, they have virtually the same meaning. 'I'm not gonna lie' tends to be more informal, however, whereas 'to tell the truth' is a more general phrase.