Yes, you always need more space in your polytunnel than you have
I've had mine for about 15 years or so Connor, and living where I do on a draughty hilltop in Scotland, at 1000', I wouldn't be growing much without it. I used to grow lots of extra for the family and to sell at the gate, but now I'm a bit decrepit I just grow enough for the two of us.
I find it's much easier to keep the weeds down inside than out as any soil without plants is dry so easy to pull the weeds out. This year mine is very crowded as I am growing just about all my veg inside, because of the past two wash-out summers when I lost a lot of outdoor crops - such a waste of work.
I have a lot of ventilation for my tunnel but even so when the sun shines it can get well into the '90s in there.
Because of the amount of wind we have here I have a small greenhouse, 6x8, inside the polytunnel for raising early seeds, overwintering some hardy things which don't like winter wet - it's unheated and still gets down nearly as low as outside in the winter, but up to 100 or even 110 degrees inside in the summer.
Something else you could try for selling on is hanging baskets. They don't take up extra space as you hang them from the crop bars, and people love to buy beautiful, ready-filled baskets, bursting with flowers and ready to hang. You could even give people a discount the following year if they bring back the used basket for you to refill