What do I do if I think I used too much Roundup

you just have to hold down the trigger till all the pressure is drained off

Since Roundup works by being absorbed by the foliage and transported to the roots, I would think that cutting back the foliage would hinder this process, so you shouldn't use the weed eater before applying the Roundup.

Any Roundup Weed & Grass Killer RTU can be refilled with the new 1.25 gallon Roundup Weed & Grass RTU Refill bottle OR use Roundup Super Concentrate (purple cap).

Directions to Refill with Roundup Super Concentrate

• 24oz RTU: 1 oz of RoundUp Super Concentrate, fill with water very slowly to avoid foaming.
• 1/2 Gallon RTU: 2 1/2 fl. oz. of Roundup Super Concentrate and slowly add 1/2 gallon of water
• 1 or 1.1 Gallon RTU: 5 oz RoundUp Super Concentrate, fill slowly with 1 gallon of water
• 1.33 Gallon (PNS & PNG): Add 6.5 fl oz of the Super Concentrate to container and slowly fill with water

I wouldn't think so.

i think it is 10ml per litre or go and look at a store that sells it and read the back of the bottle

Yes it will. Use on mature plants only

6 fluid ounces of Roundup (12 tablespoons) per gallon of water. Small weed seedlings can be killed with half this strength: 3 ounces per gallon. When using Roundup Super Concentrate, mix 2.5 ounces (5 tbsp.) with a gallon of water to control most weeds and a half-strength solution for small weeds. Roundup Pro Concentrate is the strongest solution available. Spray a mixture of 2 ounces (4 tbsp.) on weeds and half that amount of concentrate on emerging plants. Since Roundup doesn't discriminate between weeds and other plants, use the least amount of herbicide possible to protect desirable vegetation.

Roundup Concentrate Plus is the least concentrated mixable product Monsanto offers. Annual and perennial weeds can be controlled with a mixture of 6 fluid ounces of Roundup (12 tablespoons) per gallon of water. Small weed seedlings can be killed with half this strength: 3 ounces per gallon. When using Roundup Super Concentrate, mix 2.5 ounces (5 tbsp.) with a gallon of water to control most weeds and a half-strength solution for small weeds. Roundup Pro Concentrate is the strongest solution available. Spray a mixture of 2 ounces (4 tbsp.) on weeds and half that amount of concentrate on emerging plants. Since Roundup doesn't discriminate between weeds and other plants, use the least amount of herbicide possible to protect desirable vegetation.

If you're using pro-roundup or agriculture level roundup mix 1 Cup of roundup to 5 gallons of water. This will give you a mixture between 1% and 2% which will kill most undesirables and anything else that picks up the spray.