Let's see what happens next
The first time you see a 50 is scary. But it is eventually a number you are aiming for, for a nadir (the lowest point in the cycle) Next time when you get a 50, give a little bit of the regular food and retest in 20 minutes If he is headed up, wait another 20 minutes and make sure he is still going up. (3 tests headed up are what you want to see) If he is dropping and in the 40s, then give a tablespoon of the gravy off the gravy food and retest. The idea is that you don't want him to get full if he is dropping and refuse to eat because that takes away your best treatment to bring the numers up.
Today, the gravy food will probably bring him up but test again to be sure. You may see a bounce tonight from the 50. (We have been suspecting that your pre shots were bounces from low numbers.) Or he may bounce from the gravy food. Regardless I would stay with the one unit - unless he is below 200 Then please get some advice before dosing. (a 50 when you are around is one thing; a 50 and below can be dangerous at night when you are asleep)