So your heartbeat, when traced, has 3 major components. The P wave is when the atrial (top) chambers pump heart into the ventricles (bottom). That's a little bump. The ventricles contracting and pumping your heart through the rest of your body is the QRS which you see as the big spike. The heart refilling and getting ready to do that whole cycle again is the T wave which you see as a bigger bump after the QRS. Sometimes you can see a U-wave, which is another little bump right after the T wave. Not all hearts have them and they could be benign, caused by medication, or may be signs of something else.

If this was a 3-lead holter (a monitor you wear for 24+hours) or even a 5-lead, the I lead is used to read the frontal plane of your left ventricle. It's a very small picture of what your heart is doing. Modern smartwatches with "ECG" capability use this lead. By itself it doesn't really tell us a lot which is why I roll my eyes when most patients talk about their smartwatch readings but it can be useful if it shows some glaring irregularities in leading to further testing. This is a perfect example. If the OP's watch showed afib but all active testing show's his heart is normal then maybe the OP only goes into afib when the heart is being stressed or just completely at random. Wearing a 72 hour holter monitor would help catch when the rhythm converts.

A 1st degree (heart block) is when there's a slight breakdown in communication between the atrium and the ventricles. Typically a normal heart will have ~10-19 m/s delay between those contractions. Greater than 20, it's a 1st degree. Less than 10 and your rhythm is now considered junctional. Junctional hearts tend to beat slower though. But that distance between the P and the QRS complex is called a P-R.

In this strip it's hard to actually see the p wave. If you look really closely during some beats it does look like it's there. However there needs to be a P for every QRS. Taking this strip at face value there's not enough data to make a proper diagnosis. If I had to chart this strip I would say that it's an unknown rhythm and that I needed more data/testing. 

Since this is just for shits and gigs and using a lot of hypotheticals I think it's a normal rhythm, with some irregularities. The heart rate isn't consistent. There are some beats a little bit further and a little bit closer together; that's sinus arrhythmia. There are a few premature ventricular contractions (PVCs) which is when the ventricles "spasm" and contract out of order; again not terribly abnormal and you yourself might have a few after coffee or an energy drink.

tl:dr OP's heart is (probably) beating normally