Instead of lemon juice (ONLY bottled of course!) you could have used some granulated citric acid. These 'acidifers' would usually be meaured and added in each jar, prior to filling with the boiling tomatoes. Now that its in there already, you can try adding some dried garlic, oregano, and onion to 'push' that lemon taste away a little. If its only sour add a bit of sugar. Adding a little balsamic vinear, or red wine will help some, as will a small can of tomato paste. All of these together or seperatly are great additives for a spaghetti sauce.

Define too much. ;) A small amount can be countered by sugar or other seasonings as Ken suggested. And adding commercial canned tomato sauce/paste/spaghetti sauce will fix it if it was moderately overdosed.

But if you tripped and fell into the pan while carrying the open bottle of lemon juice and really let it have it ;), you can add all of the above as well as double the original recipe leaving out the added juice the second time. It just all depends on if the cost of the salvage job is worth it to you or not.

Good luck.

Dave