SUBREDDIT: r/relationships
TITLE: How do I (F/26) make it up to a friend (F/26) over my bad wedding etiquette?
POST: This will seem really petty but I was hoping I could get advice. I am about to see a childhood friend (we're both female, 26) who I haven't seen since her wedding reception 2 years ago. I have literally only talked to this friend a few times in the last 5 years but next month I'll be seeing her at a mutual friends hen party.

Even though I live in a different country and wasn't invited to the full wedding, I flew in especially for it. Basically this was my first wedding and I didn't know proper wedding etiquette. Not only did I not reply to the evening invite (I didn't realise this was necessary!?), I also didn't give a wedding gift. So I showed up unexpectedly, stayed 2 hours and gave a card with no money inside like an idiot.

Now a few years have passed and I've been to lots of weddings I've realised I must have seemed really rude and I've also heard various couples complain about guests who didn't give them adequate gifts. I feel really bad! I just asked my parents who were invited to the evening do also but didn't go, and they said they gave my friend a card with £100 inside! 

She is a lovely person and I want to explain myself/make it up to her. Is it too late?? If you were this friend what would be a good way to apologise? Would it be weird to now give her £50 in a card even though the wedding was years ago and I haven't seen her since?  I feel really pathetic asking about this but it's worrying me!
TL;DR: 
How do I make it up to a friend after I didn't reply to the evening invite of her wedding then still showed up, and also didn't bring a gift?