I've been working on a jumper with a pattern for Christmas. It involves using a few colours. I've been weaving the colours on the back of the work as this was what I saw on YouTube tutorials etc., but the part with the main pattern has gone very thick and lumpy, presumably because there are so many layers of yarn at the back. Unfortunately I can't upload a photo as they keep being over the maximum file size!
Is there a way to avoid the jumper being so lumpy?