I have a couple of squash plants growing really well up a bamboo wigwam. They have produced loads of flowers, and then start to develop small yellow squash. However, the squash don't grow more than 2-3 inches in diameter, then stop. The earliest ones have now gone a bit brown, so i took them off. There are about 10-12 other squash still on the plant. Are there too many? They are growing in our own compost in a raised bed. How do i make them grow bigger?