Help! Blow out!

My baby is wearing size two diapers in Huggies which are up to 18 pounds. I have a relatively small baby! He’s 15 pounds and 5 months old. He has blowing out his diapers up his back… I don’t think the diaper is too small. Can this happen because it’s too big?

The waist in front is tight but when I sit him up I can see there’s a gap from his butt….

What can I do?

Should I go back to size one?

Technically his weight says he should be in size two and is too big for size one… is this just a normal thing? Help?

I’m willing to try another brand if I absolutely have to… but I do have 12 giant boxes of Huggies up to size 5 😅🙈 because I did try a few brands of newborn diapers and found I liked Huggies the best for preventing the blowouts… I guess I didn’t think that it would change based on his growth…