
Pretty noob here too

. You're good to go. You want to do it, you know you should do it or you wouldn't have bought the bike, and you'll feel so much better once you start doing it.
I'd hazard a guess there are 2 reasons anyone would feel they are too fat to cycle, first they won't be able to physically do it and second they're self conscious about looking like a fat twit on a bike.
The first is simply untrue, start easy, maybe only a mile but it will increase over a few weeks and don't quit, you make massive gains in a few weeks once you start (caveat: I'm not a guru and wasn't as big as you but the first mile was still hard a couple of years ago - then it got to 2 and 3 and then 5 and 10 pretty quickly).
Counter intuitive though it may seem the second is simply untrue as well, turn the thinking on its head, by which I mean, prior to buying the bike its extremely unlikely you noticed the weight of anyone you saw riding one, same rule applies, nobody is even going to notice you, never mind laugh at you.
In fact if I do notice anyone fat on a bike these days I am far more likely to think "Good for you" than anything remotely negative.