To compare your performance with the S&P 500, I think you have to work out what you would have got at the end of the year if you had simply invested everything in the S&P 500 at the time you invested it in your portfolio (simply looking at "what the S&P 500 did" over the year is not, I think, the right thing to do).
This randomly-found site, gives historic prices for the S&P 500. Since you've given a whole year of figures, I've used the prices from 2017 and assumed you invested the amounts shown on the first of each month. The following table shows how many "nominal shares" in the S&P 500 you could have bought each month and their value as at 1st January this year (prices are to nearest $; number-of-shares to 3dp):
Month Invested S&P 500 Price Nominal Shares
--------- -------- ------------- --------------
February 500 2,330 0.215
March 1,500 2,367 0.634
June 1,000 2,434 0.411
December 1,000 2,664 0.375
Total 4,000 Total "Shares" 1.635
S&P 500 as at 1st Jan 2018 2,790
Value as at 1st Jan 2018 4,560
Profit (on 4,000) 560 or 14%
Note: I have not included the sale from your portfolio because you said you sell when you either no longer like a stock, or the price is high-enough to warrant realising gains. I think the correct way to compare your strategy with investing in the S&P 500 is to assume you left all monies invested.
(If you had sold $2,000 of your investment in October (either because you needed some "ready money", or because you thought the S&P's performance warranted selling), then: the S&P price on Oct 1st was $2,557 so you would have had to sell 0.782 "shares" to extract $2,000. This would have left a total of 0.852 shares worth $2,378 on Jan 1st 2018, for a profit of $378 or 9.45%).
How does this compare with your strategy? It depends on whether your situation matches what I think your figures are saying or not...
If I take your figures at face value, it appears that you've done considerably better than the S&P 500 – perhaps too much better, which is why I have some doubts whether what you mean by them matches what I think they mean.
If the $350 is the "paper profit" on your portfolio at the end of the year (that is, the value of your remaining shares as at Jan 1st less whatever you paid for them), and you extracted $2,000 from that portfolio during the year, then it would seem you made a total profit of $2,350, or a very welcome 59% profit.
If the $1,000 you invested in December was part of the $2,000 extracted in October, and not "new money", then you're still well ahead of the S&P 500, but not as dramatically: your profit would have been $1,350 or 34% – over double the S&P.
If the $350 is actually your total profit, including the $2,000 you extracted, then your profit would simply be $350 or 9% (very slightly below the figure if you had invested everything in the S&P and liquidated $2,000; a little under two-thirds of what you would have got if you'd left everything in the S&P 500).