First tournament as a white belt

Have a plan! Example below.
Pull guard, get to closed guard.
Drill-> How to keep them in your closed guard.
Drill-> One good sweep to get to top position (the one you already know)
Drill-> Two move submission combo from closed guard (ex. Cross collar choke&armbar OR Triangle&Armbar)
Drill-> how to keep top position and submit
WIN!
All this is very doable if you have a partner that is willing to drill if you dont have then you go there and try to win by conditioning.

The number one drawback of a first competition is dealing with nerves and adrenaline. The above reply about having a gameplan is not only a fantastic tip but can also help deal with the nerves because you'll have something to focus on which can almost turn into a mantra.

I perform terribly under any pressure and nerves are always going to happen but I've found that focused breathing exercises whenever I feel too tense really help keep tensed-up muscles more relaxed and, again, gives me something to focus on other than the what-ifs and general crap that floods your mind before competing.

Everything gets better with experience and competing is not an outlier in this, you may think there's not much you can do about this with it being your first but creating the competition conditions in training in the weeks and months beforehand can really help. E.g. start roll from standing, keep score as you're rolling (NAGA in the Gi uses IBJJF rules), knowing and rolling by the rules of the competition etc.

You haven't mentioned if you plan to cut weight but at least for first competitions don't. At your level it's not really going to matter much and the added stress and anxiety will compound to make it more of a disaster than a success.

But most importantly enjoy it, and know that if you do lose it's not the end of the world but it will go leaps and bounds to improving your Jiu Jitsu none the less.

For my first comp, my coach told me, "Don't forget to breathe." For my second comp, coach said, "Don't forget to have fun."