Did you insult its mother? Those birds hate that.
Seriously, though, you're fine. If you are a troll, then you can get a nice laugh out of this sentiment, and I hope that I've made you feel awesome. If you aren't a troll, then at least hear me out.
There is no possible way that a single bird is following you. You're totally OK. You're definitely over thinking this. I can totally guarantee that it's all in your head. Sometimes birds just hop from place to place, and it might just happen to follow your path. I suppose that it's a possibility that there is a shiny object on you, as magpies have been known to collect those.
Still, there is nothing supernatural, and there is no way that it's going to hurt you. Relax, play some games, and if you're really worried, just close the window.
Don't be afraid to send me a message if you're still worried: I've been suffering with similar obsessions for years now.