Clenched my teeth 3 times while stressed. did those few times cause my bottom front teeth to shift or does it take yrs of clenching for that to occur?

It takes much longer: than 3 episodes of teeth clenching to make your teeth shift. I suppose it takes a good number of months before this starts to occur.

Clenching!: Repeated months of clenching and gritting (bruxing) your teeth will cause shifting and a wearing of the occlusal services of the dentition. Future dental care may involve teeth adjustment (equilibration) of the dentition or the need for an occlusal guard. Try to understand cause of stress and therefore lessen need to clench teeth.

Shifting teeth: Shifting may be a response to years of clenching/grinding (3 isolated instances won't do it). May be due to malocclusion. May be early indicator of bone loss. Ask your Dentist to have a look. Protective occlusal guard may be indicated. Gum/bone treatment may be required. Orthodontic treatment of malocclusion may be indicated. Follow your Dentist's advice.