Calm down, it’s fine.

When you start off you’re going to have some muscle imbalances – It’s natural.
For me it was because I used to play tennis, which led to my right arm, shoulder, and chest muscles becoming stronger than my left side.
For other this may be due to simply writing in class and other activites which require one muscle more than the other, or having a bit too much alone time..(*cough*)

When you get into lifting you will notice that the problem tends to fix itself to some extent, due to the fact that with most exercises you’re engaging both sides of your body with equal intensity.

One thing to make help resolve the problem is by making sure that when you do exercises such as the bench press or squat, you are not using one arm more than the other; I believe this is partly the reason why people have a slanted bench press and squat when they start off.
When I see people doing dumbell movements, a lot of the time I notice that the motion of one arm is slightly different to the other – this may work one arm more, which may cause further imbalances. Beware of this and make sure the range of motion for both movements are the same.

To help fix the imbalance, what I tend to do for single-armed movements is to always start off with my weaker side, and only do as many reps on my stronger side as I did for my weaker side.
This should help prevent further imbalances. If this is not enough, you may want to try doing 1 or 2 more reps on your weaker arm than your stronger arm for a few sets.

*Or just try swapping hands for a few weeks – the secret that the industry doesn’t want you to know*

-Mike