This is my personal suggestion, you should DYOR before investing in Cryptocurrency.
I would suggest you to divide $500 into four parts, it should be $100 into 3 and $200 into a single crypto . The top four Cryptocurrency that I would recommend to you is
1. Cardano - $100
2. BNB - $100
3. Litecoin - $100
4. Bitcoin - $200
You can change the amount as per your likes. I am not going to explain to you why I choose these cryptos, if you can check google, you will get your answer. I estimate within 2 to 3 months you should be easily able to make 2x of your investment. Remember as soon as you reach 2x individually or the total balance of $500 (which ever you reach first) cash out.
to be honest I'm not a fan of multi coins trading . I pick another coin with BTC and trade it. now I'm trading in BNB.
whats your opinion in XLM ?
I am not a big Fan of Monero and since your requirement stated that you need to 2x the amount within a period of 2 months, I recommended this option. if you have already invested in BNB most of your requirement will be taken care of.
Still I would recommend you to buy Cardano, read this article to know why?
https://www.investinblockchain.com/cardano-ada-explodes-after-recent-promising-announcements/ This my personal opinion. DYOR before investing in Cryptocurrency