As a swimmer here are my thoughts:
The swim portion of a tri is really 95% mental. If it is a wetsuit legal swim remember that it's virutally impossible to drown in a wetsuit since they're so bouyant so when/if you get tired in a race - or just if your heart gets racing too much and you're having a bit of anxiety - flip over on your back and let the wetsuit hold you on top of the water while you catch your breath and slow down your heart rate.
That being said, a few other thoughts:
1. You do want to start working on building up the distance you can do before stopping. Most HIM have the bouys about 600M or so from one another (assuming it's a triangular course) so you want to know that you can comfortably swim from one to the next without stopping. Since it sounds like right now you're basically there and just stopping briefly at each 50 you want to try and lengthen it out so that you can make the whole 600M without stopping. That's honestly not as hard as it sounds. I would talk to your coach about building in ladder sets such as 50M swim, rest, 100M swim, rest, 150M swim, rest and go back down. As your endurance builds you'll be able to bump it up so that you're increasing the distance.
2. If you haven't done a lot of open water swimming I would try and get in some open water swims. If that's not possible then ask your coach about including some "siting" drills into your swims. For example, in a pool you could do 25's or 50's (depending on if you're in a 25 or 50 yard/meter pool) swimming normally, then add in a few head raises where you can see the other side of the pool, and then put your head down and practice swimming normal once again. You want this to feel relatively comfortable so that during a race you can look up and site the bouys to help keep you on the right course. The last thing you want is to swim more then the actual distance because you went off course. Remember that the shortest distance between two points is straight line so you want to swim as straight as possible from bouy to bouy.
3. Practice with your wetsuit. Best if you can get in a few swims outdoors with a wetsuit but if not then suck up the fact that you're going to look like a tool and just go to the pool in your wetsuit. Swimming in a wetsuit feels very different. Not a bad different but different (and it does make swimming much easier) so you want to know what that feels like outside of the nerves and such that come along with race day. This of course assumes the race is wetsuit legal. If it is and you don't have a wetsuit either find one you can borrow/rent that fits right. It may cost you just a little bit extra but it's really worth it if you're not a comfortable swimmer.
4. During the race break the swim down mentally just like you break down the triathlon in and of itself. Rather than looking at triathlon as a whole many people recommend mentally taking it in chunks so that 1. the swim, 2. the bike, and 3. the run. You don't get ahead of yourself and focus on the run while you're still in the water. If your not a comfortable swimmer you can do the same thing with the swim and simply focus on getting from Bouy A to Bouy B rather than focusing on the entire swim. Taking it in chunks will make it seem more manageable and not as overwhelming.
Ok, that's a lot of info. Feel free to ask me anything and I'll be happy to cyberhelp. You can definitely do this but you may want to put more of your time and effort in the next 9 weeks into the swim since it already sounds like you're well ahead of the curve on the bike. It's not about being the fastest swimmer but making sure that you feel comfortable in the water. As long as your comfortable you'll be able to finish and before you know it you'll be on the bike and zooming past all the fishies.