Paypal website payment pro sandbox not returning to my website

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ASP.NET

I am implementing the "Paypal website payment pro" in my website, but while testing in sandbox it redirects to "https://api-3t.sandbox.paypal.com/nvp" with message

TIMESTAMP=2011%2d06%2d02T06%3a51%3a28Z&CORRELATIONID=e9d9eca7daf6a&ACK=Success&VERSION=56%2e0&BUILD=1863577&AMT=75%2e00&CURRENCYCODE=USD&AVSCODE=X&CVV2MATCH=M&TRANSACTIONID=6JM048602T845381W

but it not returning to specified "return" url.

Please guys, help me to sort out this problem.

I am sending these parameters:

<pre lang="xml"><form method="POST" action="https://api-3t.sandbox.paypal.com/nvp>
<input  type="hidden" name="USER"           value="myapivalue" />
<input type="hidden"  name="PWD"            value="mypassword" />
<input type="hidden"  name="SIGNATURE"      value="mysignature" />
<input type="hidden" name="METHOD"         value="DoDirectPayment"  />
<input type="hidden" name="VERSION"        value="56.0"  />
<input type="hidden" name="PAYMENTACTION"   value="Sale" />
<input type="hidden" name="IPADDRESS"       value="59.178.92.233" />
<input type="hidden" name="CREDITCARDTYPE"  value="Discover" />
<input type="hidden" name="ACCT"            value="6011000990139424" />
<input type="hidden"  name="EXPDATE"        value   ="052016" />
<input type="hidden"  name="STREET"         value="9606 North MoPac Expressway" />
<input  type="hidden" name="CITY"           value="Austin" />
<input  type="hidden" name="STATE"          value="TX" />
<input type="hidden"  name="ZIP"            value="78759" />
<input type="hidden"  name="AMT"            value="75.00" />


<input type="hidden" name="RETURN" value="http://www.mywebsite.com" />
<input type="hidden"  name="CSC"            value="123" />
<input type="hidden"  name="FIRSTNAME"            value="MyName" />
<input type="hidden"  name="LASTNAME"            value="myLastName" />
<input type="hidden"  name="COUNTRYCODE"    value="US" />
<input type="submit" name="submit" />
</form>