Weatherstripping Headache: Looking for Advice

Hello again everyone,

I was painting my front door and noticed the weatherstripping was looking fairly weathered.

I decided to replace it and ordered this weatherstripping from Screwfix.

It arrived just today, but it won't fit into the slot at all. It falls out without a notion of gripping. I see now that the one from Screwfix states on the packet that it is for a 3 mm gap around the frame, whereas the original fitted into a 5 mm gap, but that wasn't clear from the website at all. I already cut off a bit of the Screwfix material to fit the top of the door, so returning it seems like a lost cause.

Is there anything I can do? Would sticking it in place with silicone be madness? Or should I cut my losses and order this instead from Silver's Hardware?

That might even be a better product. Would be eager to hear from other users.

Thanks again!