Big vein in right biceps

I was doing biceps curl and when i looked at my right biceps there was a REALLY big vein. Its the only one and first at that size, i really worried at that moment, i usually keep lot of water under my skin and only my medium arms, shoulders and legs sometimes shows veins, but very smooth. THis one is very big and definited, i just stopped the curl and strechted, it didnt hurt, but for sure it was no normal. Now the vein isnt really big, but still very blue. Ill try to explain better, my normal veins when lifting are the size of spaguetti, im not massive guy, but this one is the size of a pencil, must i worry?

of course not. it's just a vein.