Solo London in March

I can interpret your question in one of two ways.

One is that you will be in London for a weekend, as a detour from a work trip somewhere else. The other is that you will in London for work, and are looking to get away from London for a weekend to go somewhere else.

So, first you need to clarify which is your situation.

Second, you need to clarify what you are looking for out of the weekend. If you'll be in London, what sorts of things do you enjoy or not enjoy? If looking to leave London, were you looking for a city, small town, or rural destination? Did you want to stay in England or go to another country? Are you willing to fly?

If you are looking to get out of London for a weekend, a great and easy destination is Liverpool, which is very different from London, has lots of sights (not just Beatles-related ones, although of course they are a highlight for many), and is cheaper to boot. If you buy an Advance train ticket, even the travel there is cheap. And while hotel rates in Liverpool go up on Fridays and way up on Saturdays, they plummet on Sundays.

Rick has a very good Liverpool chapter in his England and Great Britain books (same chapter in each). I was there in September 2016; if you're interested, my VERY detailed report is here: https://community.ricksteves.com/travel-forum/trip-reports/uk-trip-report-glasgow-manchester-liverpool-in-september-2016

Another easy weekend from London is Paris. Just make sure you book your Eurostar train fares well ahead (as in right now), as these fares skyrocket closer to travel. Of course, you'll have to be very selective with just a weekend, but with good planning you can make this work well.

EDITED for clarity about Big Red's question.

I will be taking a detour from a work trip to London for a weekend in
March. Wanted to see if anyone had any good suggestions for me!

This is vague.

Since I often travel solo to London at the end of March, I'll share what I enjoy. I typically get tickets to a West End play. I revisit my favorite museums including the National Gallery, the Imperial War Museum and the Tate Britain. I take day trips which have included Oxford, Cambridge, Salisbury, Ely, Windsor and Bath. I've taken a weekend trip to York. I peruse bookstores including Hatchards and Foyles. I attend Evensong and go to Choral Eucharists on Sundays with Choirs of Men & Boys/Girls. I visit palaces including Kensington and Blenheim in Oxfordshire.