Was doing squats yesterday, noticed my muscles twitch in both legs when contracted. Stopped when relaxed. Read that contraction fasiculations can be a sign of MND. Really worried. I have widespread twitches, doc says anxiety. No weakness. No atrophy.

Trust your doctor. Motor neuron disease in a 29 year old without weakness with isolated fasciculations would be at best uncommon.
Muscle fasciulations. ...are one of the symptoms of MND (aka ALS or Lou Gerig Disease), but, unless other, more obvious symptoms occur, MND is very unlikely. Fatigue of specific muscle groups ( like when you're straining to do that last rep) can cause twitching, trembling or shaking. Anxiety can cause what is better described as "jitteriness." Dr. Anne.