Different spacing between cells with UICollectionView and FlowLayout - swift

Question

I have a problem with dynamic cell sizing in a UICollectionView, or maybe a logic problem. I would like to calculate the width of the cells in sizeForItemAt indexPath: IndexPath. I have a minimum spacing of 1. The problem is that the board/spacing between my three cells is not the same as you can see in the picture. The spacing between the first and second cell looks bigger than the spacing between the second and the third cell.
My code:
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 9
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath) as! CustomCell
cell.backgroundColor = UIColor.gray
cell.name.text = "My Textfield"
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
let width = mycollectionView.frame.width
let cellsInLine: CGFloat = 3
let widthWithoutSpacing = width - (spacing * (cellsInLine - 1))
let cell = CGSize(width: widthWithoutSpacing / cellsInLine, height: 50)
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
return spacing
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
return spacing
}