There is only one number 20 and i dont know where to connect it to.

After lots of staring and wondering, I figured this out. On the big piece that makes up the bottom center of the boat, there are labels for 19, 23, and 24, but numbers 20, 21, and 22 are missing. If you look closely, that label actually shows 19-23, 24. It means 19 through 23. You are supposed to stack up the parts labeled 20, 21, 22, 23, and 24, and connect them all to the bottom of the boat where the label 19-23, 24 appears. This worked for me - I hope it helps you or someone else who looks here when they get stuck on this same problem! After lots of staring and wondering, I figured this out. On the big piece that makes up the bottom center of the boat, there are labels for 19, 23, and 24, but numbers 20, 21, and 22 are missing. If you look closely, that label actually shows 19-23, 24. It means 19 through 23. You are supposed to stack up the parts labeled 20, 21, 22, 23, and 24, and connect them all to the bottom of the boat where the label 19-23, 24 appears. This worked for me - I hope it helps you or someone else who looks here when they get stuck on this same problem!