It is possible to go over your welds on the belts between the panels after the raft has been completed. The inside of the chambers are the fabric side so if you deflate the raft and weld the belt again with the chamber flattened it will not hurt a thing.
I have found that a pressing tool helps set the weld on the belts. I normally weld the belt the first time and then go over the entire belt one more time while the raft section is laying flat on a flat surface. I can get those wrinkles out by heating the belt and then pressing with the little pressing tool I made. here is a picture of the tool.
You can see more about this on a topic I posted as Tips and tricks.
Mike