I had the same problem (sinky legs) but found if your head is in the right position your legs stay up more. I kick a lot less now and find swimming less stressful. My swim instructor told me that some of the best swimmers only get about 10% of their propulsion from their legs.
The better I swim the less I kick and I am getting faster. I do believe there is a balance, but often find if I swim in open water (in a wetsuit) I forget to kick all together.
Train yourself to kick your legs, that will give you stability and nice body position in the water, but do not give it all during the race. Just have a nice steady effortless kicking.
Late reply and hopefully you are sorted now, but...
Swim with a pull buoy (or even 2) and learn how to use your arms effectively as it is your arms that provide almost all your propulsion.
As above, even if you are a good kicker, you will only get a very small proportion of propulsion from kicking but it is very expensive in terms of energy expenditure.
Kicking simply drains you, and its this energy sapping that is the important part you don´t want.
See: https://mastersoftri.com/triathlon-training-swimming-training-tools/ and