Greetings, and congratulations on your upcoming recording!
As others have already pointed out, you can always record another take if you mess up. As one who's done a good deal of recording (of both my own playing and that of others), I would add that recording is not like live performance, and for some it requires a different type of practicing. Allow me to explain:
First, in an audio recording, no one can see you -- this removes an entire dimension from your performance. If you are one who performs publicly a great deal, this may be irrelevant since the visual component of your playing may already have become subconscious. But if you don't play in public as often, or if you suffer from performance anxiety, it might help to leave out the thinking about the visual component of your playing when you practice - all that matters is that the notes, style, and technique are right.
Second, if you're nervous now, you'll probably be much more nervous once your friend hits the record button. It's different for every performer, but for most of the ones I know, the fact that you're being recorded and the desire to lay down that elusive "perfect take" will work against you in the studio. The key is just to remind yourself that the "perfect take" will virtually never happen - just try it a few times and choose what you like most. Consequently, in your practicing, don't stress about perfection.
Finally (and this is also psychological), keep it in perspective: since you've mentioned that this recording is primarily for family and friends, bare in mind that they will almost never be as harsh a judge of your playing as you will. It's easy to pick out mistakes in your own playing because you know both (1) your owns weaknesses and (2) all the ins and outs of the piece you're playing. But most of your listeners won't have this knowledge when they hear your recording, so they won't be as critical.
Best of luck!
LD