My first jacket, feels tight but maybe it is right?

I wear the white t-shirt, my belly gets revealed a bit when I stretch upright 🙂 Is this normal, please? But when I lean forward, it is probably ok? Generally it feels tight, I am a bit compressed. It is this winter jacket:

https://www.decathlon.co.uk/p/men-s-winter-road-cycling-jacket-racer-2-black/_/R-p-345268?mc=8911933&c=orange

Please, should I try to get the larger size? Thank you so much as this is the first road cycling jacket I bought.