Quick Organic Chem Nomenclature Question

[Batmaniac]

Homework Statement

I am to draw a structural diagram of 2,4-dimethyl-1-heptyne.

2. The attempt at a solution

----------CH3
CH=C-CH2-CH-CH2-CH2-CH3
---CH3

I tried just using spaces but it wouldn't indent them so I used hyphens. Now, I'm fairly certain my answer is correct (one of many possibilities) but I have a question about this compound. How can it have a methly group on 2 in addition to a triple bond? The 'C' in my diagram is sharing 3 electrons with the Carbon to its left, one with the carbon to its right, and one with the carbon below it. That totals to five shared electrons when Carbon wants 4. What's the deal?

 

[chemisttree]

You have an excellent grasp of the situation.