Mazal tov on your engagement!
A foreign substance on the body that is permanent and never removed is not generally considered a barrier to immersion. However, this is only true if the substance does not cover a majority of the body and if a majority of women would not be bothered by such a substance.
According to most opinions, the hair is considered a separate entity from the body. Thus, if the majority of the hair is knotted and water can not reach the individual strands (or if there is a foreign substance on the majority of the hair), it is considered a chatzitzah (barrier). Furthermore, if the majority of women would mind this and want it removed, it is also considered a chatzitzah.
Unfortunately, because most women do not wear dreadlocks and would mind having them, and also because the majority of your hair is knotted, it would not normally be permitted to immerse with your hair in dreadlocks.
We urge you to discuss this issue with your kallah teacher or local rabbi or mentor for individual guidance.
Please feel free to get back to us with any further questions.