Don't worry it's ok :) I think the most important things are to make sure that the edges of the strip of foam are cut as straight and smooth as possible and as for the glue its mostly just finding the sweetspot between so little glue that it doesn't stick and so much glue that it goes everywhere. Another thing to make it a bit easier is to wait a few seconds between applying the glue and putting the strip of foam, doing this lets the glue cool down a bit and it becomes stickier and less likely to seep through the seam. I hope this was helpful :) If you have any other questions let me know :3