This is my first post so be gentle with me!
Anyway, today I decided on a combination of Marris Otter and Crystal Malt, with a little Light Chocolate Malt and Caramel Malt.
My wort is now cool and I have just taken the OG .....it is quite a bit lower than I had calculated. The combination of shopping lists, and a moody 5yr old didn't help when I was filling the mash tun this morning. well.........a 1kg bag each of Marris Otter and Crystal got left behind

Left as things are the beer will be a little too weak for me.
I was thinking of perhaps adding some extract or DME to beef it up a little. However, I won't be able to visit the brewshop until Wednesday(Saturday today!), so it will be three days into the fermentation by then!
I have never added any extra fementables into an actively fermenting wort before, so I'm unsure what will happen.
Will this do bad things to my beer?
How will it alter the flavour?
Will it mess up the fermentation process?
Or....will it be OK?
Any ideas greatly appreciated.
Cheers