CJK -these problems with the deck are not insurmountable. Good luck with a replacement, just don't do anything so the full kit can't be returned!
For the route I recommended it's totally, easy-peasy. I hate cutting plastic kit injection mouldings, it's quite hard and thick, knives skid once and you're left with a horrid scratch to fill. You can get long sheets of thin polystyrene for a few £ (the spare material comes in handy later). Trace the kit deck onto the sheet with a propelling pencil. I cut out the new deck with kitchen scissors. Cutting new openings and gluing in some waterproofing is then a doddle on a decent cutting mat with a stanley knife, buy some 2mm square evergreen profile pack and glue that a few mm inside the new deck so the kit hull has something to conform to and it might pull most if not all the deformation out. Good strengthening for MEK or Dichloromethane solvent weld to adhere to also (don't use airfix type cement please!).
If you're a total starter what are you intending for running gear? I recommend you use a single slimline 4mm Caldercraft type shaft. Not sure on the size of your hull but I'd try and cut down and file an off the shelf brass rudder rather than make your own.
If you can save a few grams here and there it all counts on a small, fast model. And good access to the inside is key. You might also consider rationalising the amount of detail as it's everything to be damaged accidentally.
My 1:48 with the Ripmax 400 motor has 50% of the hull out of the water on full chat. About as much as the hull would take I think and much quicker than I expected -you wouldn't want any quicker on that model. Any more power, and some full speed turns generated aeration at the prop. I got 20mins out of my mini 1,600mAh Ni-Mh 7.2v stick but that was not 100% throttle all of the time.
Hopefully you get somewhere with this. Distortion is common! I always ask to open the boxes I look at to check before I buy, otherwise it's judgment if it can be fixed. I don't think you've taken the easist route as a starter though. BUT my first R/C model when I was in my early teens was the small Billings Waveney lifeboat -model shop owner laughed at me in front of my Father for thinking it could be R/C'd -and looking back it wasn't for a beginner (very thin plastic and not easy to waterproof the parts I made removable), but I did it and it sailed fine for years, and that was way before mini/micro R/C gear or Ni-Cd batteries with decent capacity was affordable to proletarians!
Hope these ideas help,
Rich