Making my moms homemade spaghetti sauce and her direction said add 1/2 c sugar for 2 qts Tomatoes. It tastes too sweet for me. Can I fix it easily?
That does seem to me to be a lot of sugar for a pasta sauce recipe; most I've seen that call for sugar at all would use at most a few tablespoons per two quarts, and even then only if the tomatoes were naturally not very sweet (i.e. the sugar would only be added if necessary).
Regarding how to fix it, you have a few possible options; firstly, as moscafj suggested in the comments, you could dilute the sugar by adding more tomato, ideally having prepared it the same way you did the original batch, up until just before you added the sugar.
The other method I'd suggest would be to try balancing out the sweetness with additional salt or acid; our tongues treat the four 'basic' flavours (salt, acid, sweet, bitter) with some degree of mutual exclusion, so the stronger one is the weaker the others will appear to be. I'd suggest you be careful with this method; if you go too far with adding extra salt and/or acid (such as vinegar or lemon juice), you might end up with something that tastes closer to ketchup than pasta sauce. I'd encourage you to go by taste; separate out a cup or so of the current sauce, taste a bit, think about whether it would taste better if it was saltier or more acidic, then add a small amount of the relevant ingredient, stir, and taste again until satisfied. Once you've got a good handle on whether your particular sauce can be rescued by this method, you can take similar steps with the full batch.
I don't know where that recipe came from (the US?), but in Italy a little bit of sugar is added only when the tomatoes are too ripe and a little bit acidic.
To fix it adding salt would not help it because salted is not the opposite of sweet. If you cannot dilute the sugar adding more tomatoes you could try and change the plate into a sweet and sour recipe adding a little bit of vinegar, many people would be horrified at the thought of the ketchup spaghetti, but that is better than the sweet tomato sauce.
Another solution could be to add a lot more basil than usual. Or, if you are still cooking the sauce you could put some spearmint, cooked spearmint sometimes give a slightly bitter aftertaste, that would balance the sweet.