What happens if i wear higher prescription eyeglasses than my actual prescription?

At most a headache: Nothing bad will happen to your eyes if your wear a prescription that doesn't match the refractive error in your eyes. All glasses do is bend light and if it's the wrong glasses for you, the light won't be bent correctly to allow you to see properly. It may give you a headache and cause eye strain, but that's the worst that should happen to you.

Nothing bad: The eye cannot be damaged if you wear a prescription that is not correct. It will certainly cause strain and possible headaches, but as long as you are an adult, the worst case will be discomfort. The one exception is that children (especially those under age 7) who are not using the correct prescription may develop permanent vision loss.