i think my dream wedding dress is too similar to my friends

I think your first paragraph about feeling really comfortable and pretty in it tells you what to do. Don't worry about her or anyone else comparing, it's your dress & your wedding so you are entitled to wear what you like.

Even if all the guests at her wedding will also be at yours, I don't think it will matter. I can't remember the details of any brides dress more than a few months after the wedding - I'll remember that she looked beautiful & happy, and perhaps the general style (strapless/sleeves, long/short, a-line/ballgown), but unless a dress is a real one-off, I wouldn't realise if two brides a year apart wore the identical dress, never mind a similar one. (In fact, I did go to a wedding where the bride wore a wedding dress that she had borrowed from another girl - the former bride was there, and most of the guests were the same. And the only reason we knew it was the same dress was because they told us! Different bride, different flowers, different accessories and styling - all made it look like a different dress)