good for you! the fact that you went on a group ride is great... it will make you stronger and you'll no doubt learn lots of skills from other riders too! When I was new I asked a TON of questions to experienced riders... I found that the cycling community is in general VERY helpful... everyone WANTED to help me learn...
and yep, repeats are excellent for training... climb, climb, climb... and you WILL be stronger... and maybe you were the last one up the hill... but you got up there!
way to go...
There is a fine line between "hobby" and "mental illness".