Yes your pot is not huge, but it is a damned sight better than the 7L spaghetti pot I used when I was doing partials, so you will be fine. I made a mild in a 19L pot with a grain bag for BIAB and won a gold in Sydney.
I should add that you might be best off substituting the kit with unhopped (nearly said unmalted
) extra-pale extract, and adjusting your grain QTY.
There is a new software program out called BrewMate which is free, I haven't used it because i have purchased Beersmith. It can help you with your calculations.
Remember that it is important to just do it, you won't make the best beer in your life right now, but it will be better than your last. It is better to just tackle these ones head-on and learn as much from each as you can. There is no point deliberating too much in the early stages (unless you are wildly off - this is where software and style guides like BJCP come in).
FINALLY - good job on tackling a partial! Once you start messing with base malts instead of just extracts, you will really learn what it is to tailor your beer to your palate. You might start off desiring a humble replica of Carlton Draught, but you might end up really learning a great deal more.