Argula, (sorry I don't know how to use the picture feature)

Here is a link that might be useful: {{gwi:32192}}

You can leave lettuce & just keep cutting young leaves & use in salad as mesclun mix. Cut with scissors leaving just the centre leaf or two, and it will regrow at least 2, maybe 3 times.

...or you can carefully transplant seedlings.

If you decide to thin out, just cut the extra seedlings at soil level with scissors - and use these to make salad.

Yeah that is way too close.

I thin to about 4-6" apart.

This was 19 days ago.

{{gwi:30716}}

This is today.

{{gwi:32197}}

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Do I just cut some of the lettuce down to soil level to try to thin my leaves?

Cut few of the leaves off the lettuce plants to use in salad, even daily. As long as you leave the centre, they will keep growing new leaves. If you want to eliminate plant alltogether, cut off completely at soil level.