Hi!
As others have said, that’s not a big rise at all for a meal with mash, so your meal dose was correct. You started off too high, so you need to ask for a correction dose. If I was at 15 before eating (this is my ratio, so please don’t take it as something you should do without discussing with your doctor), I’d need to give myself at least three units before eating, plus insulin for my meal at my normal carb ratio.
You’re doing well getting your meal ratio right early on, so well done!